The Beast's History
Before any known history, the Beast had fought against the Disciples of the Light, another force that had existed prior to the beginning of the current universe. During this battle, the Disciples subdued the Beast and ultimately imprisoned it within the bowels of a lifeless planet that remained in orbit of a black hole. How the Beast remained locked within its prison is unknown.
In the 43rd century, the rogue Time Lord known as the Doctor and his human companion Rose Tyler arrived on the Beast's prison, now referred to as Krop Tor. The TARDIS had materialized within Sanctuary Base 6, a facility where a group of humans were studying the adjacent black hole and drilling for possible resources. The drilling had awoken the long-dormant Beast, who was able to read the minds and emotions of the base crew, selecting one to possess.
After possessing the archaeologist Toby Zed, the Beast - in Toby's body - ventured out onto the planet's airless surface. He attempted to hypnotize one of the other personnel, Scooti Manista, into opening the airlock to join him, but she resisted. Angered, the Beast used telekinesis to breach the airlock by force, causing Scooti to be blown outside and die in the hard vacuum. Toby then returned inside the base and the Beast seemed to release him from its control.
Later, as the Doctor and Ida Scott were venturing towards the pit where the Beast was imprisoned, the Beast took control of the Ood, the alien slave labour force on the base. Using the Ood, the Beast began killing off the base staff. As the staff struggled to survive, the Beast would communicate to them via the Ood's telepathy, tormenting them with their own fears. In the end, Zack Flane, Danny Bartock, Toby and Rose were able to reach a rocket and escape the planet while the rest of the base personnel perished. The Sanctuary Base collapsed into the planet's interior and was destroyed.
Meanwhile, the Tenth Doctor continued to descend into the Pit while Ida remained at the edge manning the winch that lowered the Doctor down. When the Doctor reached the bottom, he found a chamber with two pillars, each holding a vase. Within the expansive cavern beyond the cliff was the Beast, chained in place and roaring menacingly. The Doctor tried to communicate with it, but the Beast said nothing back. The Doctor soon deduced that the creature before him was the body of the Beast, but its mind was gone. In truth, the Beast's consciousness was in possession of Toby, now on a rocket speeding off to Earth.
Realizing that Krop Tor was not only the Beast's prison but its lifeline, the Doctor smashed the vases on the pillars. This appeared to disrupt the gravitational field that kept Krop Tor from falling into the black hole and the planet began to break apart. The Doctor then fled from the chamber and found that the TARDIS had fallen down into the pit when the Sanctuary Base collapsed. He used the TARDIS to save Ida, then took off to save Rose and the others on the rocket.
Sensing that his body had been destroyed, the Beast's consciousness emerged from within Toby, enraged and breathing fire. As the Beast proclaimed that it was sin incarnate and could never be destroyed, Rose grabbed a nearby rivet gun and fired at the cockpit's pressurizing canopy, shattering it. She then unbuckled the safety harness on Toby's seat and the possessed Toby was blown out into space and consumed by the black hole, thus seemingly destroying the Beast. Rose, Zack and Danny were then saved by the Doctor before dying from exposure to space.
