Henry Winkler made an appearance in the Season Two episode, "City on the Edge of Forever (Flashbacks)". He appeared as Arthur Fonzarelli from Happy Days, as well as providing the snarls of the Big Black Scary Monster.
He also appears in the beginning of the Season Four episode, "Probably", where he is seen jumping over a shark with a motorcycle. Unlike the real Happy Days episode, Fonzie is brutally killed by the Shark.
He has an abnormally large nose, as well as thick eyebrows. In "City on the Edge of Forever (Flashbacks)", he wears black shades, a black (presumably leather) jacket, a white undershirt, and blue jeans.
- Jumping the Shark is an idiom created by Jon Hein that is used to describe the moment in the evolution of a television show when it begins a decline in quality that is beyond recovery.