Any weight. At heavy I've got Ali (Archie Moore) Tunney (Greb) Marciano (Louis) Foreman 2nd reign (Frazier)
Ezzard Charles, before becoming HW champion, beat: Archie Moore (3 times) Joey Maxim (3 times) Jimmy Bivins (3 times).
Joe Louis defeated former champion Max Baer in 1935. Louis won the title from James J. Braddock in 1937.
Roberto Duran vs Ernesto Marcel although maybe calling Marcel an ATG might be reaching, but he did beat Alexis Arguello so he's definitely up there.
Ha, it’s gotta be up with the best ones here if not the best , numero uno especially with so many here picking beaten fighters who don’t qualify at all as atgs Can’t get much more atg than Ali