Garry Marshall is a character, played by Paul F. Tompkins. He has also appeared on the Comedy Bang! Bang! TV show. He is a director, producer, writer, and actor, best known for creating Happy Days, Mork & Mindy, and Laverne & Shirley.
Marshall is very particular about whether or not people call him by his first name, often saying "Please! Call me Garry!" He has been on the hunt for cryptozoological creatures such as the Loch Ness Monster and the Jersey Devil. He has had a very erratic relationship with Gillian Jacobs.
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).