I think he was also one of the crew in the B52 in Dr Strangelove tooI think I really became aware of him as an actor with Field of Dreams. Once I saw him in that, I realized he had done a lot of other work, including Darth Vader. It's funny to be one of the most famous characters in cinema, but only as a voice, not a face.
I also remember him from the Conan movie, and now that I think about it, his character in Clear and Present Danger comes to mind. Great Actor. May he rest in peace.