Santa Claus

Santa Claus — also known as Father Christmas or, according to the Eleventh Doctor, "Jeff" or "Geoff" — legendarily distributed presents to good children on Christmas morning under their trees. He played an important part in the Christmas tradition on the planet Earth.

Profile
Santa maintained a workshop where he created toys. (TVC: A Christmas Story) In order to deliver presents to all children in a single night, Santa used time loops and clones of himself. (ST: The Man Who (Nearly) Killed Christmas)

Appearances
The First Doctor visited Santa Claus in his workshop and helped save Christmas. (TVC: A Christmas Story)

The Second Doctor warned Santa of a future where the toy workshop spanned over two thousand worlds and the fabric of space was being torn by his time looping. A solution was found involving a fleet of robot Santas and newly calculated, more stable wormholes. (ST: The Man Who (Nearly) Killed Christmas)

The Third Doctor and Sarah Jane Smith travelled to New York, 1822, where they met Saint Nicholas. Clement C. Moore watched them from his window, and then sat down to write Twas the Night Before Christmas. (ST: A Visit from Saint Nicholas)

Santa helped Iris Wildthyme save Panda from Mary Christmas. (BFIW: The Claws of Santa)

Impersonations

 * The Fourth Doctor dressed as Santa and snuck into the Brigadier's house with Romana in order to leave him a Christmas present. (ST: Better Watch Out, Better Take Care)
 * On Christmas Eve 2006, Rose and Mickey Smith encountered dangerous "pilot fish" disguised as Santas. (DW: The Christmas Invasion) The following year, the same robots, now under control of the Empress of the Racnoss, attacked Donna Noble and Lance Bennett's wedding reception. (DW: The Runaway Bride)