Because of the similar interior of the Time Machine, there have been reports that this series was originally meant to be an animated spin-off of Doctor Who (1963), but that William Hanna and Joseph Barbera were unable to obtain the rights. However, show developer Duane Poole has stated that this is untrue. The series was always meant to be a Happy Days spin-off.
The Fonz And The Happy Days Gang aired during Happy Days' 8th season, when Ron Howard and Don Most had both left. They reprised their roles for this spin-off.