Any fighters who after prison release became beast in the boxing ring or even world champions? Bernard Hopkins comes to mind. Who else?
I think Ron Lyle was in prison before he made it big. Plus Clifford Etienne, even though they didn't become champs.
Sonny liston was in prison, it's where he learned to box. Also even though it wasn't prison, Tyson learned to box while in and out of a kiddie prison sort of thing. Forgot what it's called LOL.