The Big Bang Theory has scored the ultimate nerdy coup: Theoretical physicist Stephen Hawking will make a guest appearance in the April 5 episode. (And as if that isn't enough geeky goodness, Star Trek's Leonard Nimoy does a voice over in the March 29 episode.)
Hawking has been invited to appear on the show before, but at the time he was too ill to make an appearance. Hawking will play himself and has already filmed his "run in" with Sheldon (Jim Parsons). Previously, Hawking has made guest appearances on Star Trek: The Next Generation, The Simpsons, and Futurama, so if this whole being a renowned scientist thing doesn't work out, he can always turn to acting.
Source: TV Guide