When the 1974 - 1984 TV show "Happy Days" was first created, there were three kids in the Cunningham family. Most fans today only remember Richie (Ron Howard) and Joanie Cunningham (Erin Moran). The eldest brother Chuck Cunningham (Gavan O'Herlihy, Randolph Roberts) was phased out. The eldest son supposedly went to college on a basketball scholarship. It was Gavan O'Herlihy as Chuck who asked to leave the series. Gavan was eventually replaced by Randolph Roberts until the episode "Guess Who's Coming to Christmas".

Fonzie ended up bringing that older brother vibe to the show. The executive producers of the show, Garry Marshall, Thomas L. Miller, and Edward K. Milkis admitted, “we realized that Fonzie was really the ‘big brother’ character that the show needed.” So he was used very well in this capacity as a brother figure.

In the final episode of "Happy Days," Howard Cunningham, the father, (played by Tom Bosley) comments that he is proud of his “two kids” and Chuck is not mentioned at all.

"Happy Days" ran for 11 seasons which means it was one of ABC’s longest running series!

More Info: en.wikipedia.org