8. Johnny Galecki
'The Big Bang Theory' star Johnny Galecki provided the voice of Arnie in season 2 episode "Irregarding Steve". Arnie is a mentally-handicapped squirrel, who is minded by his brother Gilbert (John Krasinski) who both hit the road on the back of a bus when their tree - and Steve's treehouse - is destroyed by a lightning bolt, leading to the Smiths believing Steve has died. Galecki is best known for his role as Leonard Hofstadter in the CBS sitcom The Big Bang Theory, and stars alongside Jim Parsons and Kaley Cuoco.