Intruder

Intruders were persons whose presence in a particular place was unauthorised. (TV: The Green Death)

The Eighth Doctor identified Lucie Miller as an intruder when she appeared in the TARDIS. (AUDIO: Blood of the Daleks)

The Tenth Doctor, upon using a teleport pod to enter a Sontaran flagship, was branded an intruder by General Staal. He quipped, "how did he get in, in-tru-der window?" (TV: The Sontaran Stratagem)