Locomotora Castro has announced his definitive retirement quite a few times, but he always comes back. In an interview from a couple of months ago, he said that one final fight was in the making for the end of year. Given that he won the last one, I really doubt he stays inactive for much longer (he was busy doing an argentinean reality show during this year). So I'd say that his 90 wins by KO are unmatched by any other non-retired fighter.
