<Li> Tommy (Kevin Sullivan) (seasons 8--11; 13 episodes)--Another friend of Chachi and Joanie in episodes after Richie and Ralph left the show . Like Bobby, Tommy is a student in Fonzie's auto shop class, as well as in Roger's health class . At one point, he was also on the Jefferson High basketball team, and performed in a band with Joanie and Chachi . </Li> <Li> Heather Pfister (Heather O'Rourke) (season 10; 12 episodes)--Ashley Pfister's daughter . Initially did not get along with Fonzie, but gradually learned to accept him as a father figure . </Li> <Li> Charles "Chuck" Cunningham (Gavan O'Herlihy, Randolph Roberts) (seasons 1 & 2; 11 episodes)--The oldest son of Howard and Marion Cunningham and older brother of Richie and Joanie, Chuck is a college student and basketball player . He is rarely seen and disappears without explanation in season two, never to be seen nor referenced again after "Guess Who's Coming to Christmas". The character's disappearance gave rise to the pejorative term "Chuck Cunningham Syndrome", used to describe TV characters that disappear from shows without explanation and are later retconned to have never existed . Gavan O'Herlihy played Chuck, but then he asked to leave the series . Gavan was eventually replaced by Randolph Roberts until the episode "Guess Who's Coming to Christmas". </Li> <Li> Eugene Belvin (Denis Mandel) (seasons 8 & 9; 10 episodes)--Nerdy classmate of Joanie and Chachi, and twin brother of Melvin Belvin . Is in Fonzie's auto shop class, and has a crush on Jenny Piccalo . Despite being a general stooge to his classmates at Jefferson High, he frequently tags along with Joanie and Chachi's circle of friends . </Li>

What happened to the older brother chuck on happy days
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