<P> Sandy (Yeardley Smith) is an employee at the job bank when Sheldon seeks a part - time job to clear his head . </P> <P> Susan (Katey Sagal) is Penny's mother who first appears in the Season 10 premiere "The Conjugal Conjecture" when she comes to attend her daughter's re-wedding to Leonard . Sagal and Cuoco previously appeared in the main cast of 8 Simple Rules for Dating My Teenage Daughter, in which Sagal's character was married to (and later widowed from) that of John Ritter, and Cuoco was their titular "teenage daughter". </P> <P> Trevor (Blake Anderson) is an individual with whom Sheldon has conflict when he cuts in front of them at the movie theatre . </P> <P> A number of Hollywood celebrities and famous scientists and engineers have made appearances as themselves . </P>

Actors who have been on the big bang theory