Toby Zed
The Walker Expedition's archaeologist Toby Zed labored at discovering the nameless script found on the planet orbiting the black hole designated K37-Gem-5.
Zed first heard the voice of the Beast which then possessed him. Using Toby as his vessel, the Beast murdered Scooti Manista, another member of the crew. Toby told no one. To his relief, the manifestations of the Beast's presence vanished from his body. (DW: The Impossible Planet)
Through "freed", the Beast remained free to possess Zed. As the Walker Expedition rocket left the planet with Rose Tyler on board, the Beast manifested itself in his person. Rose unbuckled his seatbelt and used the bolt gun to smash the window. An emergency window prevented the ship from de-pressurized and Toby flew through space, into the black hole. (DW: The Satan Pit)
Abilities and signs of possession
While the Beast took him over, Toby's irises turned red and the script appeared over his body. He could survive vacuum unscathed (DW: The Impossible Planet), spoke with the voice of the Beast and issue flame from his mouth. (DW: The Satan Pit).
Personality
Toby Zed had a quiet manner. While attempting to use the personal fears and weaknesses of the Doctor, the crew and Rose against them, the Beast revealed to the others that already into his twenties, Toby had never had sex. (DW: The Satan Pit)
