Or take the Rocky franchise.
IMO, the first film is great. It's more about drama than it is about boxing. I don't think Stallone is a particularly great actor, he doesn't seem to have a great range. He plays tough guys and action heroes and that's about it. But I think this actually worked in his favour in Rocky (1976) - the titular character is supposed to be an everyman, an ordinary guy who gets offered the chance of a lifetime when his life was going nowhere.
It's difficult to identify the antagonist - is it Apollo Creed? Well, Rocky fights him but Apollo's not a bad guy. He's just doing his job (world HW champion). I think all the negative factors affecting Rocky's life, added up, is the antagonist. The fight scene at the end is pretty good. Creed is a reasonable impersonation of Muhammad Ali. Rocky does his best, pushing the champ close.
https://www.youtube.com/watch?v=Q_qhLRUh66k
So, where to go from there? Well, Rocky II (1979) had Rocky winning the rematch.
Then it kinda went cartoonish in Rocky III (1982) & Rocky IV (1985).
Ivan Drago was a computer-trained Soviet fighting machine. I thought he was a good character when I was 10 but, as an adult, it's a bit lame.
https://www.youtube.com/watch?v=bdx9geh510E
https://www.youtube.com/watch?v=qZRbStnLn3c
I thought Rocky V (1990) was pretty crap and I haven't seen Rocky Balboa (2006) or Creed (2015), although they're supposed to be good.