A wild guess would be Davey Moore (the one brutalized by Duran). I'm not confident at all in that pick however.
Shorter then that. I met this guy a couple of times during his career. He won the title then lost and retired.
For shortest amount of fights in a career for a undisputed champion (not ABC) how about Jimmy Carruthers World Bantamweight Champion 25 contest's in career, 21W 4L
Bukkake, im never going to forgive you. I went to say leo randolph before you even posted and thought that would be the only time i would get a question right that H asks.