You obviously haven't heard him as the joker. I never knew it was Mark Hamill till i saw him talk about it in an interview.
This. I never knew until way after the Batman cartoon ended. His work in Arkham Asylum/City is awesome. Out of all the major cast (except maybe Billy Dee Williams) I think Hamil would be the only one even willing to touch it. It's below Harrison Ford and probably even Carrie Fisher.