Charles "Chuck" Cunningham is the oldest son of Howard Cunningham and Marion Cunningham and the older brother of Richie Cunningham and Joanie Cunningham. He was played by three different actors. In the "Love and the Happy Days" pilot, he was played by Ric Carrott, but in the first two seasons of Happy Days, he was played by Gavin O'Herlihy, who was replaced by Randolph Roberts for two episodes in the second season.
Chuck Cunningham was a high school jock at Jefferson High, who was known for making rare appearances at home. Almost always seen with a basketball, he shared an upstairs room with Richie until he went away to college, possibly on a basketball scholarship. Richie briefly stays at his place for a time. He had a big appetite and was often eating when he wasn't shooting baskets off the garage. One Christmas, he recommends to his father to get Fonzie to fix the family Santa Claus display. Chuck also tends to suck his thumb when he's worried, a trait he shares with his sister, Joanie Cunningham.
- Chuck 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". A way to describe TV characters who simply disappeared from shows or were dropped or forgotten to the point where later episodes of the show are 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. However, it should be noted that the series had a hard reboot between Season 2 and Season 3. This was to accompany Fonzie becoming a regular character as a big brother to Richie and his friends, effectively erasing Chuck from existence and making the reboot a completely separate series from the first two seasons (effectively creating a separate TV series). After this reboot, the series also went from a traditional comedy to a comedy that shifted between drama and slapstick. This is evident by the fact that in the final Happy Days episode at the end of Season 11, Howard comments that he's proud of his "two kids," acknowledging that Chuck never existed in this iteration. Likewise, many of the incidents and events in the first two seasons are never mentioned or described later in the series.
- Both Gavin O'Herlihy and Randolph Roberts were re-united with Marion Ross in the Happy Days: 30th Anniversary Reunion.