BoxRec

- Back in the day when Ali was a staple of free airwave broadcast TV, he initially couldn't appear in the US as the Champ because of NOI associations that sent him to Montreal vs George Chuvalo, London vs Henry Cooper and Brian London, and then Karl Mildenberger in Germany.

Mildenberger was promoted as an soccer player, but he was actually an accomplished Lefthanded EU Hvy. Other than SRRobinson's one title fight with a lefty, the boxing landscape was bereft of quality Left fighters because trainers would convert them to Rightys so they could make fights since MGRs didn't want their fighters to look bad vs Leftys.

Texas with it's new Astrodome offered him a venue whereupon he moved and bought a home in Houston where his mangled Bio Fantasy was produced that I may have been a part of in a public setting. Strictly cornball stuff then sorta like now.

Anyway, Ali looked bad vs Mildenberger who got on top of him that had Howie Cosell choking on his toupee before an Ali combo saved the day.

Any other Lefty Hvy Contenders before that? I reckon right around the 2000s Leftys in all weight divisions started appearing, the best ever being Manny Pacquiao. I know Lewie fought one and looked like doodoo...

Mildenberger was the first to fight for the title, and gave Ali some problems for a while until he got figured out. The most prominent before him would have been Melio Bettina, but only dipped in and out of Heavyweight with varying degrees of success.

Ironically the first southpaw HW champion, Michael Moorer, was actually right-handed.

Not sure who that makes the first naturally southpaw champion.

it didn't happen, but
Corrie"The Sniper" Sanders was scheduled to fight Michael Moorer
for the title he had, but Sanders had broken his leg while doing roadwork and the fight was cancelled, so Moorer fought
"Big" George Forman instead

1960s British Heavyweight Jack Bodell was a southpaw.

James J. Jeffries was naturally left handed but he fought in orthodox style.