Santa Claus

He turns up on a rooftop with a sleigh, elves, and enormous good humour, insisting he's exactly who he says he is even when everyone around him assumes he can't possibly be real. Loud, warm, and quick to laugh at his own absurdity, he barrels into the Doctor's world uninvited and refuses to leave.

Nick Frost plays Santa as if daring the show to take him seriously, and the trick is that it does. He's funny in the way a big, confident performance is funny, but underneath the jokes about tangerines and naughty lists there's real warmth, and Frost never lets the joke curdle into mockery of the character himself.