Saul Montana?
The thread about the Old West in the 'Other' forum made me think about ol' Saul and him being the Mexican Heavyweight champion seemingly forever.
Mexico is/was the best place to really build a career in boxing if you think about it. What boxing was in the States before the Muhammad Ali Act with less strict commissions and virtually every town having shows, you can find competitors of every conceivable level there.
A complete novice with zero amateur experience, can just walk into a pro ring and fight another complete novice, and build up your record and skills in relatively quick fashion. Chavez had 44 fights before he ever won his first title, because he started literally from zero in all aspects.
It's incredible Montana fought from '88-2016, albeit most were against nonentities in his later years. I remember watching him on TV alot as a teenager.