Garry Marshall is a character played by Paul F. Tompkins. He has also appeared on the Comedy Bang! Bang! TV show. He is a writer, producer, director, and actor, possibly most known for creating the TV shows Happy Days, Mork & Mindy and Laverne & Shirley.
Mr. Marshall is very particular about whether or not people call him by his first name, often saying "Please! Call me Garry!"
He is a being (possibly an alien?) from another dimension. He lists the eight dimensions as Peanutbutter (our dimension), Tipsy Topsy, Melon Bank, Egg Town, Little Egg Town, two others he can't remember, and an eighth one no one knows about (which is where he is from).