If you don't know his name you've heard his voice.

Most popular as Brain on Pinky and the Brain with a voice that sounds eerily like Orson Welles (he did Orson's voice in the movie Ed Wood in fact.)

Has really dozens of voice-over credits in various animated series--He's Kif Kroker and (I think, although I can't prove it yet) Calculon in Futurama and played the garbageman on the ill-fated Dilbert cartoon. His IMDB writeup goes into horrific detail about his career. He's apparently very adept at imitation and mimicry.