Half of XL bully dogs in Britain are descendants of one “killer” inbred pet from the United States that has produced generations of violent animals, it can be revealed.
Extensive genealogy research seen by The Telegraph shows how decades of inbreeding has created a narrow gene pool of unstable fighting dogs that have become responsible for 70 per cent of dog attack deaths in Britain.
XL Bullies are now among the most fashionable breeds in the country, with puppies selling for more than £2,500 to families who are told that they are placid pets that are safe around children.
But ministers are concerned by a series of high-profile incidents in which the dogs have attacked strangers in the street, mauled toddlers and torn apart other pets.
After a video posted online showed an XL Bully attacking 11-year-old Ana Paun and two men who tried to defend her, Suella Braverman, the Home Secretary, announced that she is considering an outright ban.
Researchers have now identified one dog from Los Angeles that may be responsible for dozens of violent incidents.
Publicly available pedigrees of British “stud” dogs, used for breeding, show that half of pets on the market are descended from the dog “UKC’s Most Wanted Kimbo”, known by breeders as “Killer Kimbo”.
Kimbo’s size and strength, produced through generations of inbred fighting dogs, has given it legendary status in the XL Bully community.
Gustavo Castro, the dog’s breeder, grew up and lives in the Huntington Park neighbourhood of Los Angeles. His Facebook page shows pictures of him lifting the dog and it sitting on his sofa.
Kimbo was the product of two dogs from the same parents, and is thought to have bred hundreds of XL Bully puppies, passing on an extremely narrow gene pool that experts have warned can make dogs unstable and cause genetic diseases.
Researchers from BullyWatch, a campaign group, say that dogs related to “Killer Kimbo” are responsible for at least 10 violent incidents worldwide, with dozens more impossible to trace.
The Telegraph can reveal that the death of Keven Jones, a 65-year-old former lorry driver from Wrexham, was caused by a dog linked to Kimbo.
Mr Jones died of blood loss after a dog bite in May last year from his son’s XL Bully, named Cookie Doe, which was related to Kimbo on both sides of its family.
Deaths attributed to the dog’s descendants also include Mia Derouen, four, who was mauled at her home in Louisiana in 2014 by Niko, an XL Bully bred directly from Kimbo.
Doctors were unable to save Mia, who was locked in a bathroom with her mother to protect her from the out-of-control dog. When police arrived, it took 12 rounds of bullets to kill the animal.
The same fate befell an 82-year-old woman in Oklahoma in 2017, who was mauled by another dog believed to have been related to Kimbo while out for a walk near her home.
Gloria Zsigmond, a UK-based scientist and campaigner for BullyWatch, has dedicated hundreds of hours to researching XL Bully dogs in Britain.
She told The Telegraph she was concerned by the number of dogs related to an animal with a history of violence in its bloodline.
Using family trees uploaded by breeders, she found that more than half of a sample of 50 stud dogs advertised online were descendants of Kimbo.
“A lot of the time, the Bully breeders are trying to hide how inbred the dogs are,” she told The Telegraph.
“Kimbo bled into all those bloodlines because he was early on and he was so dominant in breeding. There are some good bloodlines where Kimbo isn’t there, but there are many where he is.”
Her research shows that of the 50 breeding dogs, 32 were related to Kimbo.
“Kimbo’s offspring became very, very popular and they’re still so popular in the UK to this day,” she said. “It’s extremely troubling.”
Online adverts for the dogs are littered with references to Kimbo offspring – named the Unstoppable Juggernaut, the Joker and Frank Sinatra – while other breeders talk of rumours of a stash of Kimbo’s frozen sperm that could be used to produce more dogs.
One stud from Croydon is related to Kimbo on both sides of its family, while another in South London has Frank Sinatra as both its maternal and paternal grandfather.
“[Kimbo] is a real notorious one,” said Colleen Lynn, founder of the non-profit group DogsBite. “If you look at the pedigrees of the American Bullies that have killed in the US, that dog is in there.”
There is similar concern among some breeders. Andre Smith, owner of the Los Angeles-based Big Gemini Kennels, said that Kimbo’s owner should have stopped breeding the dog once the first attacks were reported.
“Kimbo is known amongst a lot of the breeders as ‘Killer Kimbo’ because his offspring have been documented to carry a rage that is not normal in the XL American Bully breed,” he told the Telegraph.
“There have been kids that [were killed] by his dogs. “
Mr Castro could not be reached for comment at his California home.
The dominance of one dog in the ancestry of violent animals in Britain was caused by the rapid expansion of the breed in the United States.
American Bullies were created on the west coast of America in the early 1990s, by breeding American Staffordshire terriers and American pit bull terriers – both of which are illegal in the UK under the Dangerous Dogs Act 1991.
The breed became popular with Los Angeles rappers, who showed off their powerful pets in music videos, and among basketball and American football players.
Realising the popularity of their creation, breeders worked to exploit the trend by producing different colours and sizes, including the infamous “XL”.
American Bullies were first imported into the UK in 2015 by Noble Welch, a breeder who admits there is a “fine line” between the breed and pitbull terriers.
He claims to have fought several court cases to overturn a ruling that American Bullies were “pitbull-type” dogs already covered by the Dangerous Dogs Act.
Since then, breeding American Bullies has become a multimillion-pound industry, with dogs and their frozen sperm flown all over the world to breeders obsessed with their dogs’ “bloodlines”.
A popular stud dog can be rented for thousands of pounds each time to “backyard breeders” in Britain who produce XL Bullies for sale in their own homes and sell them online on unregulated websites.
Kimbo was among the first to become a prolific breeding dog across the world, as the craze for powerful pitbull-type dogs spread.
Although the dogs are not recognised by the American Kennel Club, owners groups and fan clubs quickly grew into an official American Bully Kennel Club, which was founded by Dave Wilson.
Mr Wilson is widely credited with producing some of the first American Bullies at his kennel, Razor’s Edge, and said that they were no more dangerous than other breeds.
“Statistically, it doesn’t add up,” he told The Telegraph. “There are no actual statistics that tell you this is an aggressive dog, because the numbers alone show to you that this dog is not aggressive.”
But so far this year, almost half of injuries from dog attacks were by the breed, which make up about 1 per cent of the UK’s dog population – making them around 270 times more deadly than the average dog.
“This is exactly what you’d expect from a fighting breed that has been inbred repeatedly for exotic styles, colours and sizes,” said Dr Lawrence Newport, a legal academic who supports a ban on the dogs.
“We found this, of course, to our terrible cost.
“It has only been a few years since we’ve allowed a single pitbull-cross into the country. And the effects have been very immediate and devastating.”
On Thursday, a British dog-walker said that he backed a ban on the XL Bully after one savaged his cocker spaniel-dachshund.
“I’m a dog lover, but these aren’t dogs,” said Leo Wolfe.