The Beast in the Devil Chained Up
The Beasts species is unknown as he lived before space and time and matter. In some Ancient Scripts a race called the Valtino said that the Beasts Planet was Krop Tor. They say the Black Hole was a mighty Demon because it had swallowed Krop Tor but then spat it out because it tasted like Posion. Krop Tor was part of a prison built by a mysterious figure called the Disciples of Light. The Disciples of Light had ganged up on the Beast which was millions of years before. If the Beast escaped then the gravity field would stop and the Planet would be sucked ito the Black Hole. When the 10th Doctor fell into the Beasts Prison there were 2 vases and they both lit up. When a group of Humans landed on the Planet the Beast was woken up because of their drilling which the Beast had plotted the escape from his Prison.
Even though the Beast was chained up it could still use its Intelligence on the minds of others. Which he made the Base's Work Forece the Ood turn against them. You knew this because the Ood's eyes turned Red. He also Possessed one of the Humans Toby Zed and he killed some Humans. The Doctor had just thought that if the Beast was free he would go into the Black Hole but if that happened then the Planet would go with him to. So the Doctor broke one of the Vases and sent the Beast spinning into the Black Hole. Then Toby who was Possessed almost killed the Survivors of the Santuary Base until Rose shot threw the Window and un clicked his belt. Toby as the Beast was sucked ito the Black Hole. But the Beast lives through out the Cosmos as he is a Mythical Figure. The Beast has Psychic Powers that's how he got to the Ood and Toby Zed.
He has appeared in Series 2: The Impossible Planet and the Satan Pit