For the life of me, I NEVER Can remember that guys name. Another whose name I can never recall was in loads of Humphrey Bogart movies, the little actor from Hungary? the one with the bulge eyes.
Karl, you may be thnking of Peter Lorre.
Another actor who played both sides is Gilbert Roland. He was in a few westerns and played an Indian in Cheyenne Autumn. His co-star, Ricardo Montalban, is another. But I can't think of anytime he played a cowboy.