http://www.youtube.com/watch?v=6rju49vkaao
Jim Rash’s role as Dean Pelton on Community is a prime example of someone who started off as a recurring supporting character on a series, but eventually caught on strong enough that he earned himself the status of full-time cast member on the show. A similar thing happened on a much smaller scale when Rash had a bit part on an episode of That 70s Show as a pissy jewellery store clerk named Fenton, who eventually became a recurring character that appeared in six episodes of the show over the course of four seasons, and had a running gag where he was constantly feuding with Fez.