>>90031769Jack Nicholson started acting in 1956. He worked continuously from that time through his work on Batman in 1989. Hightlights include Terms of Endearment, The Shining, and One Flew Over the Cuckoo's Nest.
He had been nominated for an Oscar 9 times, winning twice prior to his 1989 role.
Sir Ian McKellen also started on film in 1964, though had previously been a stage actor.
Prior to his initial role as Magneto in 2000, his major film roles included Gods and Monsters, Last Action Hero, and Six Degrees of Separation. Much of his early career was spent in England. He had not earned any major American film awards prior to his X-Men film work.
Patrick Stewart also began acting on film in 1964. His most notable roles prior to X-Men included Star Trek, Robin Hood: Men in Tights, and Moby Dick. He had earned an Oscar nomination, and won an Emmy for his role in Moby Dick prior to X-men.
Samuel L. Jackson began working on film in 1972. His major roles prior to Iron Man include Kill Bill Vol. 2, The Incredibles, Star Wars, Die Hard with a Vengence, Pulp Fiction, Jurassic Park, Patriot Games, Goodfellas, Coming to America, and School Daze. He earned an Oscar for Pulp Fiction, and received three Golden Globe nominations prior to his work in Iron Man.
Unless someone can name someone more prolific, I'd say Jack has the competition licked. Longer career with more awards prior to his cape role, and it was at a time when cape movies weren't a thing.
