Happy Days began as a separate skit within an episode of the anthology show Love American Style. It happened to coincide with a resurgence of interest in all things from the 1950's, thanks in part to the success of George Lucas's American Graffiti (the show even took as its theme one of the most famous anthems of the time, Billy Haley & the Comets' "Rock Around the Clock," in early episodes). The show was an instant hit, and within a few years was the number-one program in the United States.
The main breakout character of the show was Arthur Fonzarelli, aka Fonzie, aka The Fonz (played by Henry Winkler). He was a tough- acting high school dropout who tooled around on his motorcycle, and who always wore a black leather jacket (though in some of the first episodes he wore a regular, light-colored jacket). Fonzie became a pop-culture idol, selling posters, lunchboxes, bubblegum cards, paperbacks, and the other usual merchandise; kids across the country adopted his thumbs-up gesture and his use of such slang as "Aaayyyyy!" and calling socially inept kids "nerds."
Happy Days lasted for ten years, finally ending after its main protagonist (Richie, played by Ron Howard) had left the show. It had kept going for 255 episodes, but by the end of its run, the basic cast and premise of the series were barely recognizable. It spawned no less than four spinoff shows, all sitcoms: Laverne and Shirley was a long-running hit for ABC; Mork & Mindy launched Robin Williams to stardom; less well remembered are Joanie Loves Chachi and Blansky's Beauties. An animated cartoon, Fonz and the Happy Days Gang, ran for two seasons on the same network in 1980-1982 - it featured Winkler, Howard, and Danny Most (as Ralph Malph) reprising their roles from the regular show; Fonzie even had a dog named Mr. Cool.