Recurring character

A recurring character is a fictional character, usually in a prime time TV series, who often and frequently appears from time to time during the series' run. Recurring characters often play major roles in more than one episode, sometimes being the main focus.

Recurring characters usually start out as guest stars in one episode but continue to show up in future episodes if the storylines or actors are compelling enough. Sometimes a recurring character eventually becomes part of the main cast of characters; such a character is sometimes called a breakout character. Some notable examples of main characters who were originally recurring characters are: Leo Chingkwake on That '70s Show; Angel and Oz on Buffy the Vampire Slayer; Marc St. James on Ugly Betty; Vanessa Abrams on Gossip Girl; Zack Allan on Babylon 5; Steve Urkel on Family Matters; Donna Moss on The West Wing;Michelle Dessler and Chloe O'Brian on 24; Santana Lopez, Brittany S. Pierce & Blaine Anderson on Glee; Lois Lane & Oliver Queen on Smallville; and Kimmy Gibbler on Full House.

...
Wikipedia