Seven Guest Stars Who Blew Our Minds on The Big Bang Theory

Charlie Sheen! Stan Lee! Bill Nye! Watch our favorite surprise celeb moments from the series

LEVAR BURTON

You may know him from Roots or Reading Rainbow, but Trekkies know him as Lt. Commander Geordi La Forge from Star Trek: The Next Generation. "Surprisingly it only took gas money and the promise of free food to get him here," jokes Sheldon (Jim Parsons) on episode 7 of season 6, where Burton (who also made a cameo in season 4) appears briefly as himself on Sheldon's YouTube show Fun with Flags.