Alexander Armstrong voiced Mr Smith in The Sarah Jane Adventures, Sarah Jane's Alien Files, and the Doctor Who episodes The Stolen Earth/Journey's End. He appeared in Doctor Who again as Reg Arwell in The Doctor, the Widow and the Wardrobe.
In addition to acting, Armstrong is a well-known comic and presenter. He wrote and starred in The Armstrong & Miller Show with his longtime comedy partner Ben Miller. In 2009, Armstrong and Miller's work on The Armstrong & Miller Show won them a BAFTA for "Best Comedy Programme." He is the presenter of BBC1 gameshow Pointless, including the Doctor Who edition of Pointless Celebrities .
He is a second cousin of Imogen Stubbs.