30 Rock Wiki

John Lithgow is an actor who appeared in the 30 Rock episode "Goodbye, My Friend," which also featured a clip of him in Harry and the Hendersons. In the episode, Lithgow gets lost in 30 Rock, but his presence nevertheless inspires Liz Lemon to do the right thing. 

Lithgow previously starred in the sitcom 3rd Rock from the Sun, a similar title to 30 Rock.