Catherine Tate

"All the funny stuff's down to Catherine Tate. I'm just her bitch."

- David Tennant

Born in 1968 as Catherine Ford, Tate is a British comedienne. Having played guest roles in The Bill (who hasn't in the UK?), her big break came with The Catherine Tate Show. Her most notable character from that was schoolgirl Lauren, with her Catch Phrase "Am I bovvered?"

Her next well-known role was playing Donna Noble in a well-received Doctor Who Christmas Special in 2006. She was brought back in 2008 as a full-time companion of the Doctor, and ended up becoming a fan-favorite character thanks to her performance as well as some much-needed Character Development.

She had a similar experience with the American version of The Office, first making a guest appearance in the final episode of season 7 then returning in season 8 as a major character. - This actor provides examples of:
 * Catch Phrase
 * Christmas Cake: Donna in Doctor Who.
 * Punctuated! For! Emphasis! - it is quite possible that she provided the only recorded silent example of this trope, courtesy of soundproof glass.
 * She Really Can Act: Got a lot of this with her turn as Donna Noble in Doctor Who.
 * Vitriolic Best Buds: Any time she's sharing a scene with David Tennant (and they have quite a bit), they're almost always on the opposite ends of a snark-off. Then they got to do it onstage as Benedick and Beatrice, in the RSC's Much Ado About Nothing.