Chuck Cunningham

Charles "Chuck" Cunningham was a rarely seen "Happy Days" character who disappeared without explanation after Season 2, his disappearance giving rise to the pejorative term "Chuck Cunningham Syndrome" to describe TV characters who were dropped from shows without any In-Universe explanation or sendoff, with later episodes of the show scripted as if the character had never existed. The most popular explanation for his absence is that he went off to college on a sports scholarship. Fonzie became a regular character as a big brother to Richie and his friends, effectively replacing Chuck in the little role he had in the series. In the final episode of Season 11, Howard comments that he's proud of his "two kids," indicating that Chuck never existed.