Mr Popplewick was the identity used by the Valeyard while in the Matrix. Popplewick Senior, Junior and very Juniour were Victorian Clerks and claimed to be an assistant to "Mr. J.J. Chambers" in the Fantasy Factory. They were stickler for procedure witch they used to delay the Sixth Doctor and sported an explosive quill behind the ear.
Popplewick was held hostage by Sabalom Glitz, and his true identity was revealed by the Sixth Doctor, who pulled off his mask. He declared that he knew as the performance was too perfect. (TV: The Ultimate Foe)