Stunt double
From Tardis Wiki, the free Doctor Who reference
Stunt doubles are people hired to perform stunts for an actor. The stunts they perform are usually deemed too dangerous for the actor or require certain abilities. The double must look similar to his counterpart. Often shots from behind are used for scenes with double so only the hair has to be similar. They most also look Similar to the Actor so the audience doesn't spot it in the show.
