Surprised no one’s responded with this so far, but I nominate:
Edward Norton.
He’s arguably one of the most talented actors of his generation.
He broke onto the scene more than 20 years ago as the lead (opposite Richard Gere) in Primal Fear. He was so good, he received an Oscar nomination (Best Supporting Actor) in essentially his first-ever role.
Incidentally, he won that role against none-other than Matt Damon.
His very next film? Working with Woody Allen in Everybody Says I Love You.
Two years later? A well-deserved second Oscar Nomination (this time for Best Actor) for American History X.
Which he followed by co-headlining Fight Club with Brad Pitt.
The problem?
Eventually his ego got the better of him.
He’s smart, really smart — went to Yale, speaks Spanish and Japanese — even worked in Japan for a while before taking up acting.
So he tends to want to do script work on his projects. Sometimes this works (like the uncredited re-write he did on then-girlfriend Salma Hayek’s Frida). Sometimes not.
This came to a head with his work on The Incredible Hulk (2008). While he did well in the role, apparently he clashed so much on-set with one of the producers — insisting on several script elements and generally being a diva — the studio re-cast him for the next film, The Avengers.
As of 2017, he’s still around – but mostly in supporting roles.
Since 2008, I can’t think of a major film he’s headlined.
He still does great work (such as receiving a third Oscar nomination two years ago for Birdman), but he’s now mostly relegated to supporting roles (such as in The Bourne Legacy or Collateral Beauty), but ten years ago he easily would have been in the running for the lead in either.
Consider that he’s a contemporary of Matt Damon (with whom he starred as the co-lead in Rounders in 1998). But today – comparing their respective trajectories, it’s easy to see that Norton — easily the greater talent — has seen his career suffer for other reasons — his ego, arrogance, and reputation for being a jerk.