Finding Kimbo

At Bully Watch, we began delving into the pedigrees—essentially, the family trees—of dogs from the most well-known Bully XL kennels across the UK. Our investigation steered us down a trail where one name recurrently surfaced in the lineage of numerous dogs. It was a name that has gained infamy in the United States. A name that left us speechless and sent a cold shiver down our spines. One we never expected to uncover.

The name of Killer Kimbo


On March 25, 2014, four-year-old Mia Derouen and her 27-year-old mother, Megan Touchet, lived a typical life in their apartment complex in Houma, Louisiana. One crisp afternoon, Megan put on music, danced with Mia, watched TV, and began folding clothes. Their family dog, Nico, a 60kg Bully XL, suddenly started barking, an unusual behaviour for the normally mild-mannered two-year-old dog. When Megan investigated, Nico’s expression was unlike anything she had seen before.

Despite Nico’s history as a loyal and gentle companion, Megan instinctively felt danger. As she tried to grab Mia and step in to the safety of the bedroom, Nico, positioned in the living room, closed the distance between them with unexpected speed. Despite Megan’s attempts, Nico’s imposing frame forced its way into the room, and he focused his attack on Mia.

The subsequent events are too horrific to detail. Eventually, Megan managed to escape through the bedroom window with Mia. She handed her severely injured daughter to paramedics, who rushed her to the hospital with critical facial and head injuries. Tragically, Mia did not survive.

Police arrived to secure the apartment. Nico was shot three times from outside by officers. Undeterred, he charged at the officers as they attempted to enter the apartment, prompting them to shoot him ten more times. The officers later described the scene as “horrific”, and counselling was provided to all those affected.

To this day, Mia’s stepfather maintains there were no prior signs of aggression from Nico. He recalls the dog’s sudden and inexplicable change in demeanour as if he had been possessed by a demon. He believes that such an instant transformation could only result from aggressive traits in Nico’s bloodline. This theory is bolstered by rumours that nearly every dog from Nico’s litter would eventually be put down.

Looking at what transpired that day and what followed, he might not be far from the truth.

BTM Kennels 

Nico was, by all accounts, an incredibly attractive XL Bully. He was just 20 points away from winning a category in a show organised by the American Bully Kennel Club (ABKC), the premier international kennel club for dogs of his breed. He was bred by BTM Kennels, known for breeding XL Bullies in the Baton Rouge and Houma areas. In the aftermath of Mia’s death, BTM Kennels turned their Instagram page to private and never again conducted business under that name.

In time, the identity of Nico’s father was uncovered.

One Killer Kimbo.

Killer Kimbo 

Kimbo, known as UKC’s Most Wanted Kimbo, was widely regarded as one of the most impressive studs in the bully breeding world. Bred by Gustavo Castro, Kimbo’s unmatched size and build kept him in constant demand.

However, Kimbo was a product of aggressive inbreeding. Most reputable kennel clubs advocate for maintaining a low Coefficient of Inbreeding (COI), ideally not exceeding 20%. For context, a sibling or parent-offspring mating would result in a 25% COI. Yet, Kimbo’s COI was a staggering 31.3%. This excessive inbreeding is evident from his pedigree, where the same great-grandfather appears four times. Kimbo was born from a brother-sister pairing, and his grandparents shared the same father. He was deliberately inbred to promote a large, muscular frame. There were rumors that Kimbo’s papers were forged—a practice not uncommon in Bully breeding—potentially indicating an even higher COI.

On April 9 2014, two and a half weeks after the death of Mia Deouren, Castro defended Kimbo against accusations of human aggression. Asked about Kimbo’s inbred pedigree – Castro did not respond. Asked if he would continue to breed Kimbo, Castro did not respond. Castro would continue to use Kimbo as a stud until at least 2017 and his other dogs much later than that. Given that sperm can be frozen for 15 years, it’s possible Kimbo could still be bred from even today. 

A String of Attacks

Warnings about Kimbo were conveyed to Castro as early as 2008. Experienced owners and XL breeders had already begun sharing concerns on American Bully forums about issues with his offspring. These dogs were severely inbred, to the point that some had Kimbo himself appearing four or five times in their pedigrees. One member noted that there were two aggressive dogs from the same litter, one of which displayed violent behavior before reaching one year of age. Another member mentioned how one of Kimbo’s brothers had severely injured someone’s leg. Yet another pointed out that multiple dogs from the same litter had to be euthanized. The patterns were alarming—sudden unprovoked aggression in dogs from several different litters, all linked to Kimbo. One forum member warned Castro not to breed from Kimbo, cautioning that “a child was going to get killed one day.”

These concerns were brushed aside. Castro disregarded the complaints, and Kimbo continued to be used for breeding.

However, everything changed after the unprovoked attack on Mia Derouen.

The spotlight was turned on Kimbo. Owners and breeders began documenting severe incidents involving his offspring. The owner of an American Bully kennel was attacked by his own dog, a son of Kimbo. Another instance involved a descendant of Kimbo attacking its owner when the dog was only eight or nine months old. Time after time, cases emerged of attacks involving Kimbo’s direct descendants.

Kimbo’s bloodline was linked to over ten documented attacks, but due to his pervasive presence in a multitude of Bully XL pedigrees, the actual number could be much higher. One person who’s been documenting issues with this bloodline asserts there have been over 30 attacks associated with it. Most of these alleged attacks were reportedly unprovoked and occurred even with good owners in positive environments.

Four months later, in 2016, a dog descended from Kimbo attacked a group of women, one of whom was the owner. In the owner’s words, “Scarface just went crazy and started attacking.” There was no provocation. The police shot and killed the dog at the scene.

In 2017, an 82-year-old woman was mauled to death by a dog believed to be from Kimbo’s bloodline. That same year, another grandson of Kimbo (from Juggernaut) attacked a young boy after escaping from his kennel. In 2016, Megan Millner, aged 38, purchased two XL Bullies from Mega Built Bullies (MBB). In 2020, one of them brutally killed her while she was out walking the dog. MBB was found to be breeding dogs which were related to Kimbo.

Finding Kimbo

A few days ago, we found ourselves silently observing an Instagram Live session featuring four different Bully XL breeders—three from the UK and one from the US. They were engaged in a frank discussion about their anticipated breeding programs’ future prospects. One UK breeder unfurled his dog’s pedigree, essentially a large piece of paper charting a family tree, and pointed to a name a few generations back: Kimbo.

With a level of confidence that was somewhat startling, the UK breeder declared his desire to return to breeding from Kimbo’s line. The reaction from the US breeder was instantaneous and startling. Her face fell, reflecting what could only be described as utter horror. After an awkward silence, she firmly advised the UK breeder not to deal, under any circumstances, with any bloodline stemming from Kimbo.

This incident brings us to a fundamental flaw in the ongoing debate about inherent aggression in dogs. In the UK, there is practically no awareness of the troubling impact of Kimbo’s bloodline. Several UK breeders continue to disregard Kimbo’s disturbing legacy, choosing to incorporate his offspring into their breeding programs. The allure of Kimbo’s bloodline, renowned for its formidable size and sturdy build, seems to eclipse any underlying issues.

Perhaps this lack of awareness and irresistible allure explains why, when you start looking, you find substantial evidence of Kimbo in UK bloodlines.

MBB King Marshall 

Miki Wills is the Director of the United Kingdom Bully Kennel Club (UKBKC). Since the official Kennel Club of the UK won’t accept American Bullies, this is the UK equivalent. You won’t be able to find his name on the UKBKC website though. For some reason the UKBKC keeps the names of most of its staff quite hidden from public view. (Perhaps because one of its judges was exposed by panorama for illegally cropping ears.) You can quite easily find the Director of the official Kennel Club. (Hello Tony Allcock OBE if you ever read this) Despite being the Director of the UKBKC, Companies House lists Miki’s occupation with the UKBKC as a fitness coach. 

Miki was also the director of a company called Bullies and Luxury Ltd. Looking at the Bullies and Luxury website, you find its home to a number of sought after studs and dams – one of which is MBB King Marshall described as one of the “most impressive merles to walk the planet” boasting a stud fee of £10,000. 

MBB King Marshall’s mother, known as MVP’s Dolly Parton, reveals an interesting lineage. Tracing the family tree back three generations, one finds the names Kimbo and his progeny, the Unstoppable Juggernaut. Examining the full pedigree discloses Kimbo’s lineage repeated four times across five generations. You also find MBB Camo, King Marshall’s paternal grandmother, which was the dog who’s offspring killed Megan Millner in 2020.

Another notable dog from the Bullies and Luxury line is Cersei, who goes by the nickname, the Ice Queen. Kimbo’s legacy is so prominent that one doesn’t need to delve into her family tree. They unabashedly advertise this lineage as a selling point. As their website proclaims, “With 3 x UPL’s Unstoppable Juggernaut, this girl indeed has game.” It’s important to note that the Unstoppable Juggernaut is a descendant of Kimbo. Kimbo, in fact, is Cersei’s paternal great-grandfather, great-grandfather again, and also the grandfather of Cersei’s maternal grandmother.

Both Cersei and MBB King Marshall also share roots that trace back to authentic fighting pitbulls. Dogs that were active in the pits during the height of dog fighting. As if a direct connection to Kimbo wasn’t enough.

Another UK breeder called Master XL Bully Kennels makes pedigree tracing much easier for us. He lists it for us. Here’s the descendants of Axel on their website. Notice how often Kimbo and his offspring appears. We traced the pedigree anyway and its an example of how UK breeders are purposefully trying to breed monsters. Kimbo is already inbred. Breeders are taking him and inbreeding even further.

Axel’s pedigree stands as a distressing example of irresponsible breeding with seemingly no consideration for the health and temperament of the dogs produced. Brace yourself: Axel’s grandmothers, Havana and Red Snow, are full sisters, their father King Kronos doubles as Axel’s great-grandfather. His grandfathers Frank Sinatra and Kronos are full brothers. Further entwining this lineage, Axel’s remaining grandfather also descends from UKC’s Most Wanted Kimbo, due to a father-to-daughter mating. So, every grandparent of Axel traces back to Kimbo. In effect, purchasing a puppy from Master XL Bullies Axel equates to unwittingly playing the Kimbo lottery.

In the UK, we believe the majority of dogs can trace their origins to a limited number of foundation animals. The dogs that were imported back in 2014 to 2015. Looking as far back as 5-6 generations, it becomes evident that the same dogs recur consistently in every dog’s lineage. However, one dog stands out among all – Kimbo. These came be found in popular stud dogs such as Bossy’s Bullion and Tribe Bully Kennel’s D’artagnan. Kennels such as Lionslair, South London Bullies, Exclusive Bullies Inc and TopGun Bullys were all found to be breeding dogs which were descendent from Kimbo.

Deed Not Breed

In American Bully breeder forums across the US, dropping Kimbo’s name invariably sparks a fiery debate. Indeed, in the right forums, the discourse can evolve into quite a nuanced conversation about human aggression, genetics, and bloodlines. There is a faction of US breeders deeply invested in the well-being of the breed and are actively participating in a study to investigate potential genetic issues with Kimbo’s offspring. They are also probing whether there might be something akin to the A22 gene in Belgian Malinois or rage syndrome in Cocker Spaniels prevalent in the American Bully population. They have examined other bloodlines and documented incidents involving dogs attacking people, suffering mental breakdowns, or killing other dogs on their premises. Many argue that temperament testing and selective breeding should now be the top priority, even ahead of physical health and structure.

The key takeaway here isn’t to hastily label every descendant of Kimbo as defective. That’s not the case. It’s obvious that the number of generations removed will significantly influence the outcome. The crucial message is the undeniable relevance of genetics. This understanding is vital if we are to engage in a reasoned discourse on why a large number of XL types are displaying unexpected and sudden aggressive behaviour in the UK. We know that in the UK, dogs are being bred with a high prey drive and have difficulty handling arousal. The discourse in the US is miles ahead the UK.

The discourse here in the UK lacks such nuance. There’s no discussion about Kimbo. Instead, breeders fall into two distinct categories. Firstly, there are pandemic-era breeders who seem more focused on profit than breed health, with little understanding of genetics or temperament. They operate under the illusion that XLs were bred to be affectionate family pets, an idea bolstered by a network of illicit fertility clinics ready to stake their claim on the breed’s popularity. Secondly, you have the experienced breeders, many of whom are part of the UKBKC circuit. These breeders are aware of Kimbo’s lineage and actively seek it. We do not mince words here: we firmly believe that the majority of XL breeders have no regard for the breed’s health or the law. A staggering 99.7% of those advertising on Pets4Home were found to be unlicensed. Of the top kennels we examined, only one appeared to hold a council breeding licence, a legal requirement.

When we consider the US experience with genetic defects in certain bloodlines and observe who is breeding XLs and American Bullies in the UK – and the extent of inbreeding – it becomes a powder keg, especially when one considers the stance of organisations like the Dog Coalition. This group, which includes the RSPCA and Dogs Trust, seeks to repeal breed-specific legislation (BSL). The RSPCA’s principal argument is that “breed is not a good predictor of risk of aggression”, a mantra they’ve recited at every documented attack or fatality involving an XL Bully.

The RSPCA seems to be debating BSL as if we were still in 2019. The academics lobbying for the repeal of BSL rely on data on dog attacks that only extend to 2018. However, the exponential growth of the XL Bully population since its importation in 2014 has entirely shifted the goalposts in the BSL debate. (It’s worth noting here that the UK Bully is arguably more inbred than its US counterpart due to a smaller gene pool, but that’s a topic for another post). Those who base their arguments on outdated evidence and neglect the breed’s history risk tarnishing their reputation as reliable policymakers.

What does the Evidence Tell Us 

Stuart Ritchie, a Science Editor at the Independent, provides an insightful analysis of why the evidence surrounding dog behaviour is not definitive. There are a multitude of conflicting studies, and numerous investigations conducted with larger datasets suggest breed does indeed influence behaviour. Research published this year by the Royal Veterinary College found that golden-coloured Cocker Spaniels were much more likely to display aggression. Meanwhile, UC Davis found that the presence of an A22 genotype in Belgian Malinois correlated with behavioural issues.

Which brings us to the American Bully and the American Bully XL. What evidence do we have about their behaviour? Surprisingly, nothing. No academic study that we could find included a dataset featuring the Bully XL or American Bully breed. They could be the most docile breed or they could be the most violent. For anyone to claim that the science is conclusive enough to support a stance against breed-specific legislation (BSL) is profoundly misleading.

What we do know, however, is that the American Bully appears to be a significant outlier in any dataset. The breed has likely been responsible for 14 deaths in the past three years. Just last week, they killed seven pet dogs in the UK. According to our own tracker of attacks this year (now exceeding 450 incidents), they have been involved in 45% of them. When you consider the US experiences of potential human aggression and instability from Bully XL bloodlines, and the fact that people there discuss it openly, it makes you think. These are virtually the same dogs we have here. And yet, we still believe it has to be deed not breed.

16 September 2023: An Update

A lot has changed since we first posted our article on Kimbo. We have learned that Keven Jones, 62 from Wrexham, was killed by his son-in-law’s stud. A stud directly related to Kimbo. Next level Cookie Dough. The death was described by family members as an accident.

We also believe a large proportion of the Bully XL population in the UK can be traced back to Kimbo. We analysed the pedigree of 50 studs available on Pets4Home. 32 were found to be related to Kimbo. Sky News recently featured a Bully breeder on to defend the breed. He appeared with his stud (Ted) which was related to Kimbo unbelievably recently. He was pairing and breeding dogs with Kimbo from both sides.

Breeders have a lot to answer for. To say breeding in the UK has been bad is an understatement, it has been criminal. The breeding of dogs with very recent fighting lines. The breeding of dogs with problematic bloodlines on both sides. Someone needs to be held accountable for this. Let’s start by shutting down the UKBKC.

17 September – Update

The group named in the article above looking into the possibility of A22 have reached out to us. Anyone with a Bully breed which would want to support the A22 study, please contact

Participants are requested to test their dogs using the UC Davis A22 test and then complete a follow-up questionnaire based on the results. The aim is to better understand the genetic basis of certain traits across breeds, enabling more responsible and ethical breeding and informing owners of potential behavioural propensities in their pets.

11 responses to “Finding Kimbo”

  1. Great article to get this information out there. However, I believe it needs to be edited to refer to these dog’s behavior as rage syndrome and not human aggression. The behaviors are in fact VERY different. A human aggressive dog is just that! They do not just decide one day that “hey I don’t like people anymore”. Human aggressive dogs do not like people outside of their family unit; those they were raised with and around. These Bullies did not display any human aggressive behaviors prior to the incidents when they suddenly snapped! This is because that is how rage Syndrome works. The dog suddenly is no longer stable. Something within the dogs brain suddenly misfires and the dogs become uncontrollably aggressive to anyone and anything in their path! The dogs remain in this mindset until they are euthanized! It doesn’t come and go! Hence the term sudden onset rage syndrome. There is without a doubt a genetic link here and these breeders do not want their animals tested because you will take away their money! Once Science inexplicably shows their dogs are flawed? Thats it game over for them and they will have lost hundred of thousands. They are so consumed with money and popularity that they will just continue to deny deny deny!! None of them see any issues because these dogs do not display it until it is too late. There have been more deaths in the US since this was written too. Gatorhead bullies caretaker is deceased because of being mauled while caring for the dogs alone. All swept under the rug and they continue to breed and sell related animals. It’s disgusting quite frankly and why after 25yrs of breeding? I walked away from these dogs. I refuse to be apart of any of it!

    • This is exactly what happened with red cocker spaniels. Bred for colour only they inbred & they developed “cocker rage”. A previously happy dog suddenly becomes a total ball of angry uncontrollable rage. There is no cure, they can’t stop & only solution is to pts. Humans have done this, the dog always pays the price.

  2. You present this as a dichotomy; support BSL or go full in with the RSPCA line. In truth the best option lies in the middle. More control of breeders in the long term and special conditions placed on XL bullies, especially those whose pedigree shows concern.
    Simply banning the whole breed doesn’t work. If we follow the pedigree argument here why aren’t you banning Spaniels and Mali’s?

    • Its not really all that easy for a 15kg Spaniel to kill a person like it is for a 50kg Am Bully, and the A22 gene in malinois is able to be tested for.
      Most these XL bully breeders can’t even follow the law regarding breeding licenses, there’s slim chance they are going to follow these “special conditions”, and you cannot expect the government to supervise every Am Bully breeder.
      More laws will only really affect those already obeying the law.
      Im not sure what “more control” and “special conditions” you think will manage to solve the problem, but its a complete waste of resources for the government to manage every single XL bully born, and its not as though pedigrees can’t be faked or that they cant just breed without a pedigree or create a new registry.

  3. I am a dog owner to 2 Great Danes but have read this post word for word and am shocked that in this day and age in-breeding is so prolific.
    I had a beautiful Mantle Great Dane and she had a tendency to be a bit unpredictable at times, thankfully we always had her on the lead as I felt I’d done something wrong with the training of her. She was very gentle but for no reason she lunged at a spaniel who was just sitting nicely with its owner. When I looked into her breeding I found that all but 1of the litter had the same trait and also the same allergies and all but 1 has had to be put to sleep because of Osteoporosis. The breeder was made aware and she has chose to ignore this knowledge and has carried on breeding from this line. UK kennel club DON’T want to know so sadly pet lovers like myself will continue to buy dogs without having first done their homework.
    I’m pleased to say I made it my business to DO my homework, I now have a well balanced healthy Great Dane who’s breeder is available should I have a concern.
    Sadly looks like MONEY IS THE ROOT OF ALL EVIL.

  4. This is really distressing information but inbreeding between brothers and sisters etc is still going on in all breeds. I’m a St Bernard, licensed breeder, we breed health tested, low inbreeding coefficient puppies but they are more expensive than most. I recently saw a litter on the kennel club for sale with inbreeding of nearly 25% – both parents of litter had the same father but the kennel club still approved the advert!!!
    You’re right, hardly any dog breeders are licensed but not just XL BULLY breeders , it’s all dog breeders. Also RAGE SYNDROME is being found in many other breeds too.
    Yes I agree XLBULLYS should no longer be bred due to the close I breeding and the rage syndrome but you have to start st the source, the unscrupulous breeders whom are just in it for the money and whom are selling pups that are potential killers. These dogs were bred to fight , they were breed from fighting dogs, it’s their instinct.
    How many more people have to die or be seriously injured????
    To anyone looking to buy a puppy of any breed, please do your research, ask questions, a responsible breeder will help you, ask to see pedigrees, inbreeding coefficient, are they licensed but also expect to pay more for a properly bred puppy. Also choose a puppy that fits in with your family, they all have different exercise needs etc…be prepared for months of training too.

  5. I totally agree, I bred Rhodesian Ridgeback puppies. I can honestly say, more than half that had a puppy, came back for another one and all we’re disappointed when i stopped breeding.

  6. Wow what a read i have a few friends that have dogs and the XL’s and im not gunna lie they would lick you to death so to speek, there was alot of info in there and to me it seems ALL ABOUT THE MONEY, these TWATS who are in breading need dealing with thats the place to start. Make it so they haft to complete the testing that is needed, why cant that be the law, sorry to say it but the dogs dont no any different. They probs dont even see the dogs that are there sister and mother or dad and grandfather if you get what i mean. Its the dogs i fill sorry for and the GOOD BREADERS out there if there is any of the XL bullys out there this post seems to say there isn’t. Please people if your going to get a pup do as much research as you can untill your board of it. And when you much so you can write a book then go buy the right dog for you, happy pup hunting people 😊

    • So does all this mean that the aggression that comes from some of these XL Bully type dogs and any breed is all down to a certain chromozone that they get from interbreeding with other family members/siblings and only a few have this gene to suddenly go into Attack mode,.i am not a very good reader but it was very interesting read,i am a very big dog lover i have 3 dogs myself 2 Border collies and a Fox Red Labradour who when out on walks have quite a few Bullie XL Bullie friends and they are such loving dogs with the best owners they could possibly have,but i have witnessed some abusing there dogs kicking/punching/yanking on their leads and it really upsets me to see this happening and i have interviened the owner but it can be a risk as ive had abuse and threats about it,not from the dog itself but the Owner,i thought maybe this aggression in these so called dogs is from the way they are hadled by the irresponsible Owners they Have caring for them in the wrong way,Thank you Keighly,

  7. This is an extremely serious scary situation I used to have a golden cocker and yes she did display rage but I never would of thought the reason behind it was her genes infact the vet at
    The time laughed and asked if she had cocker rage since she passed I’ve always had Dobermanns and still
    Have but we also have a sbt as I was bought up with the breed but these xls are totally something different the size alone
    Do some damage but throw aggression into the mix and it’s a ticking
    Time bomb I see so many young lads with these dogs and I don’t think they actually know the capability of them it’s all about who’s got
    The biggest and bestest looking dog. What idiots

  8. A very good read and the findings about inbreeding doesn’t surprise me I am pretty good at reading pedigree papers and I know a lot of inbreeding goes on particularly in the show world. I no longer show (rough collies) due to being sold a pup from a big breeder/ champion show judge, only when I received the pedigree seen my pup was from father to daughter mating and when I did genetic test for PRA (progressive retinal antrophy) my pup tested positive for the gene. I never bred from him even although the father I also discovered had a detached retina and was still being used for stud. I kept him solely as a pet and stayed with working collies (border collies all from farm stock) The problem is these big breeders it’s all about money not health.

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