I’ll throw Jimmy Ellis into the discussion. In 1964 he’s a middleweight losing to Don Fullmer, Hurricane Carter and George Benton. By 1967 he has beefed up to heavyweight and in that year defeats Leotis Martin, Oscar Bonavena and Jerry Quarry in succession. Then he beats Floyd Patterson for the WBA heavyweight belt, his only losses from 1970 until he runs into Earnie Shavers in mid-73 are to Frazier and Ali, with a win over George Chuvalo (in Canada) as the highlight of that period. Ellis is probably the unlikeliest heavyweight champ of all, given that he was a middleweight of modest accomplishment (splitting a pair of fights with Holly Mims being his high-water mark at 160).
I would pick Leon Spinks as both the biggest overachiever and one of the biggest underachievers, somehow.
Good choice. Oleg's nickname should have been "The Cat", as the man had 9 career lives. Mike Weaver (kind of like Oleg, except Oleg always seemed to get KOed on national TV). Weaver started his career with a 1-3 record, was 6-6 after 12 fights. Talk about someone "finding themself", Weaver should be the poster child. Leon Spinks and the original Cinderella Jimmy Braddock all good choices.
If Jack Sharkey was an arch underachiever, then perhaps Johnny Risko and Tom Heeney were arch overachievers. They had a fraction of Sharkey's talent, yet they occupied a similar position in the division, while Gene Tunney was champion.
Why in god's name do people bring Sharkey into this conversation? The guy was talent rich, and kept losing crucial fights, to people with a fraction of his talent. He should have cleaned out the other contenders while Tunney was champion!