By the time 1980 rolled around, Happy Days already had spawned a pair of successful spinoffs, Mork & Mindy (1978) and Laverne & Shirley (1976). You had to figure that sooner or later, some genius might come up with the idea of putting Fonzie (Henry Winkler) in his own series. And, so they did. Sort of.
Hanna-Barbera obtained a license from Paramount to produce the animated Fonz & the Happy Days Gang, which wasn't exactly an accurate title, since some of the gang were missing. Instead, they lifted the core concept of Josie & the Pussycats in Outer Space (1972), only this time, Fonzie, Richie Cunningham (Ron Howard), & Ralph Malph (Don Most) were lost in time, thanks to a bumbling time traveler from the far future, Cupcake (Didi Conn, later of Benson & Shining Time Station). Fonzie was also given a canine sidekick, Mr. Cool (Frank Welker), who copied most of his owner's mannerisms, but was more of an annoying presence than that other celebrated pooch of the period, Scrappy-Doo. Somehow, Potsie must've missed out on the fateful day when his buds disappeared. Either that, or Anson Williams wasn't interested in the project.
Anyway, our 5 intrepid adventurers spent 2 seasons (21 episodes total) trying to get back to Milwaukee, circa 1957, as explained in the opening narrative by radio legend Wolfman Jack (The Midnight Special). For kicks, they threw in incidental music more closely associated with H-B's superhero series, such as Super Friends, and, obligingly, Fonzie was seen swinging on curtains, among other things, to nail the villains. He was, after all, the star of the show. One has to assume they eventually made it home, because in 1982, Fonzie was added to Laverne & Shirley's animated series. Not that it helped that series, since it was cancelled after the '82-83 season.
Oh, of course, Mork & Mindy would also get the cartoon treatment, also in 1982, after the live-action series ended, with the title characters (Robin Williams & Pam Dawber) rebooted as high schoolers. Naturally, that didn't sit well with fans, and Mork said "nanu-nanu" one final time at the end of the season.
In case you wonder, Cartoon Network doesn't have Fonz in its library (CBS-Paramount owns the rights), so even though the series marks its 30th anniversary this year, don't look for it to turn up anywhere anytime soon. Unless some enterprising soul at CBS-Paramount decides to release it on DVD.
Updated, 8/28: Here's the show open, uploaded on YouTube by Generic0001: