Charles "Chuck" Cunningham (Gavan O'Herlihy, Randolph Roberts) - Elder son, college student and basketball player.
Chuck's a rarely seen character who disappeared without explanation in season two, giving rise to the pejorative term "Chuck Cunningham Syndrome" to describe TV characters simply disappearing from shows, to the point where later episodes of the show are scripted as if the character had never existed.
For example, in the last Happy Days episode, Howard comments that he is proud of his "two kids". Fonzie's character took on the role of big brother to Richie and his friends. He sucks his thumb when he's worried, and so does Joanie Cunningham-Arcola.