A breakout character is a character in serial fiction, especially a member of an ensemble cast, who becomes much more prominent, popular, discussed, or imitated than expected by the creators. A breakout character may equal or overtake the other characters in popularity, including the protagonist.[1][2] Prominent breakout characters will often make cameo appearances in expanded franchises or feature as main characters in spin-off installments of their own.
Originally, the Arthur "Fonzie" Fonzarelli character was to be a comic relief dropout type, put there for comic contrast to the whitebread Richie and his pals. He was a tall, lanky guy, but when Henry Winkler blew everybody away at his reading, they decided to cut Fonzie down to Henry's size. Ultimately, Winkler molded the character around himself and everybody, including Ron Howard, realized this would be the show's "breakout" character.