He was 42 years old.
"One of the most popular MMA fighters ever, Kimbo was a charismatic, larger-than-life personality that transcended the sport. Outside of the cage he was a friendly, gentle giant and a devoted family man," said Bellator MMA President Scott Coker. "His loss leaves us all with extremely heavy hearts, and our thoughts and prayers are with the entire Ferguson family and all of Kimbo's friends, fans, and teammates."
Local media reports said that Slice, whose real name is Kevin Ferguson, had been hospitalized earlier Monday in South Florida. His official website also confirmed his death.
Sgt. Carla Kmiotek told CNN police in Coral Springs, Florida, did not receive any police or EMS calls to Slice's residence before he was hospitalized.
There is no police investigation, she said.
"We battled inside the cage, warrior vs warrior," said UFC figher and hall of fame member Ken Shamrock. "REST IN PEACE KIMBO SLICE. May God Watch Over You."
He is survived by six children -- three boys and three girls -- according to his website.
The 'Undisputed online king'
Slice, who is originally from the Bahamas but lives in Miami, compiled a 4-2 record in fights tracked by UFC
and a 5-2 record overall, according to Bellator MMA.
Standing 6'2'' and weighing around 230 pounds, Slice was known for his power and brute strength.
He last fought on February 19.
"I enjoy kicking ass," he told comedian Jimmy Kimmel. "I really enjoy doing what I do."
But unlike most in the sport, his rise to fame preceded his career in professional fighting -- Slice became an internet sensation by starring in bare-knuckle fights, often conducted in backyards, posted online.
Rolling Stone called him the "Undisputed online king of the underground bare-knuckle world" in 2006, before he began fighting professionally.
His physically imposing nature and internet fame helped create a mystique surrounding the man -- and his fighting prowess. Combining those factors with a natural charisma that endeared him to fans, Slice was able to draw more attention from the media than most fighters with his experience would.
"We just felt like he was so marketable," Jeremy Lappen, the head of fight operations at Elite XC, told ESPN's E:60 program.
Before fighting, Slice went from being homeless to working as a bouncer for a porn company in South Florida.
He told ESPN
in a 2008 interview that to him, fighting was a cathartic practice.
"I had to fight with myself not to hurt people, some serious mental wars," he said. "But who would have raised my boys? They would have grown up knowing their dad died another violent death. They would have been angry, and now, instead of one person dying a violent death, you've got two other little protégés who would have grown up just as violent and vicious, causing even more harm to people. I couldn't have that. I've got to be a guide to my kids. Nobody else is going to do it."