His role in Star 80 is my favorite performance of all time. He plays one of the most disgusting sleazebags to have ever set foot in Hollywood (Paul Snider, read up on him) with such conviction and dedication it's mind blowing. The movie's a bit like Taxi Driver except Travis Bickle is at least a cinematic character with some likeability/intrigue, whereas Paul Snider is just pure filth.
His second greatest role is in Runaway Train where he plays a simpleton idealistic convict who escapes with a bitter, gritty convict (Jon Voight) who get stuck on a runaway train. Both actors got Oscar nominations for this now largely forgotten classic.