Open Question: What’s a major star's most slept-on great performance?

Earlier this week, I wrote an appreciation of the late Diane Keaton via a look at her recently re-released 1987 documentary Heaven. I spent some time watching some Keaton films I'd never seen before and with her 2011 memoir Then Again. Keaton is amazing in Alan Parker's 1982 divorce drama Shoot the Moon, in which she plays the put-upon wife of an acclaimed writer (Albert Finney, also great) who decides not to be put-upon anymore when they separate. In Then Again, Keaton more or less hand waves the film away along with some of her other early '80s efforts because of its commercial underperformance, which is a real shame. It's stunning, on-the-edge work that finds her pushing against the limits of her established on-screen persona. I know I'm not the only person who's rediscovered the film in recent years. Now let's get the ball rolling on some other great, underseen performances from major stars. What other stars have put in great performances in movies not enough people have seen? (Waiting for Scott to show up to talk about Vin Diesel in Find Me Guilty.)