Paul Briggs was involved in organised crime back in the day. Worked as a heavy for drug dealers. Illicit debt collecting, intimidation and that kind of stuff I think.
Someone else already mentioned him but it is remarkable that James Scott fought the majority of his career whilst actually in prison. It is even more unusual in that he reached such a high level. Truly odd.
Andrew Golota... Was friends with one of the highest known Polish Mafia bosses, fled Poland to the USA cause he was getting in trouble countless amounts of times, impersonated a Police Officer and got arrested. Golota did countless stupid ****, it wasn't just in the ring his stupidity appeared Bowe was a bad dude as well. Sucker punching Larry Donald, throwing glasses, and even kidnapping his family.