12. Lou Diamond Phillips
24's lead actor Kiefer Sutherland appeared in a number of notable films towards the end of the 1980s, including Stand By Me, The Lost Boys and Young Guns, where he shared the screen with a number of other up-and-comers from the era, such as Charlie Sheen, Emilio Estevez and Lou Diamond Phillips. Best known for his portrayal of ill-fated rock musician Ritchie Vallens in La Bamba, Phillips drifted towards obscurity somewhat in the 90s (as did Sutherland and Sheen until 24 and Two and a Half Men came along), though he did pop up in Courage Under Fire. Despite this, he was still one of the actors to be credited as a 'special guest star' when he appeared in 24's first season. Here he played Mark DeSalvo, the warden of an underground prison that Dennis Hopper's Serbian terrorist Victor Drazen is delivered to. He isn't a resident for long, as his son attempts a rescue operation, resulting in a standoff that has both DeSalvo and Drazen held hostage by opposite sides. This ends messily when Drazen's captor, none other than Jack Bauer himself, opts to release his captive to secure DeSalvo's safety. Played for a fool, however, he then has to watch as the warden is shot anyway, and the Serbian criminal escapes.
11. Nick Offerman
Breakout characters are roles that are initially written as supporting or minor but eventually become a highlight and/or main attraction of a series due to a combination of the character's appeal and the actor's portrayal. From Fonzie and Stewie Griffin to Barney Stinson and Butters, every long-running comedy show seems to have one. Parks and Recreation has Ron Swanson. Deadpan and masculine (in his eyes at least), Swanson has made people take note of Nick Offerman, otherwise known for a bit part in Sin City and a handful of roles in films such as 21 Jump Street and The Lego Movie that he has won in the aftermath of his television success. Less known is his role in 24's second season, where he didn't even get given a surname during his three episode stint as 'Marcus', a citizen who reacts with hostility towards Arab-Americans following the detonation of a nuclear bomb over the Mojave desert.