The Beast (Doctor Who)

"I am the rage, and the bile, and the ferocity! I am the Prince, and the fool, and the agony! I am the sin, and the fire, and the darkness! I shall never die! The thought of me is forever: in the bleeding hearts of men, in their vanity, and obsession, and lust! Nothing shall ever destroy me! NOTHING!"

- The Beast through Toby Zed

The Beast is a gigantic demon that appears in the British sci-fi series, Doctor Who, appearing in the episodes "The Impossible Planet" and "The Satan Pit".

Origin
The origins of the Beast are a mystery, but he claims to have been born before the universe began and is the basis of every religion's concept of a Devil. What is known is that the Beast was captured by the Disciples of the Light and chained inside a pit deep within the planet Krop Tor which is able to orbit a black hole without being sucked in.

Encounter with the Doctor
When a Torchwood exploration group arrive to Krop Tor, with the Tenth incarnation of the Doctor and his companion Rose Tyler appearing, the Beast saw his chance at freedom and possess the mind of Toby Zed and then the Ood to serve as his Legion while making it seem that he left Zed's body. Managing to calm everyone down when the Beast preys on their insecurities, the Doctor has Ida rig up the loose cable so he can explore the pit to find the Beast while the others manage to escape with Rose realizing that something is amiss.

Finding the Beast after detaching the cable to reach the bottom, the Doctor learns that Beast had transfered his mind into Toby's body to escape and that was chained was a demonic body that acts on base instinct. The Doctor realizes that the Disciples of the Light arranged for oxygen within the Beast's prison so someone can destroy the source of Krop Tor's artificial gravity to thwart the Beast's escape as his mind and body are still linked. As the Doctor destroys the gravity with the Beast's body screaming with Krop Tor is sent falling into the black hole, the Beast's mind with Toby violently reacts to the turn of events before Rose sends the demonic vessel out into space to be sucked into the event horizon.

Trivia

 * The Beast is the father of Abaddon, the main antagonist of the first season of Torchwood.
 * The Beast is voiced by Gabriel Woolf, who also voiced Sutekh in the Classic seaons of Doctor Who.