Sutekh

Sutekh was an evil Osirian who planned to destroy all life in the universe. He feared all forms of life which might one day challenge his hegemony and so became Sutekh the Destroyer, the destroyer of all living things. This included his home planet Phaester Osiris and Mars. He was known throughout the Galaxy by many names, including the Typhonian Beast, Set, Sadok, Seth and Satan.

He was also the brother and husband of Nephthys.

History
Sutekh's brother Horus and the remaining 740 Osirians tracked Sutekh down to Ancient Egypt and used their powers to imprison him in a pyramid on Earth. The Eye of Horus, located on Mars, beamed a signal to suppress Sutekh's powers and hold him prisoner. The tales of the Osirians were remembered in Egyptian mythology and Sutekh was able to gain followers, like Ibrahim Namin. In the year 1911, the archaeologist Professor Marcus Scarman discovered the inner chamber of the Pyramid of Horus, discovering Sutekh and allowing him a chance of escape. Scarman's corpse was used to construct Osirian service robots and a rocket aimed at the Eye of Horus on Mars. Though the Fourth Doctor attempts to destroy the rocket eventually succeeded, he was taken over by Sutekh's will and made to take Scarman and the Robots to Mars with the TARDIS. Though the Fourth Doctor attempted to stop them, Scarman succeeded in destroying the Eye and freeing Sutekh. Hurrying back to Earth, the Fourth Doctor was able to defeat the freed Sutekh by trapping him in a time tunnel for thousands of years — longer than the lifespan of an Osirian. (DW: Pyramids of Mars)

Powers and abilities
Sutekh possessed immense power: he was shown to be able to change the course of history and destroy entire stellar systems. He was even able to contain the explosive force of gelignite although this placed a considerable strain on his abilities, and could be easily distracted when doing so. The Fourth Doctor took Sarah Jane Smith to an alternate 1980, which was a ruined and abandoned wasteland. Other evidence would suggest that it is very dangerous and difficult to change the future but a being of Sutekh's power was capable of destroying it.

He was incredibly powerful and easily able to defeat a Time Lord. His powers became apparent when his eyes glowed green allowing him to leave a person in agonising pain. He was quite able to leave a person in tormenting pain for centuries. Furthermore, his mental abilities allowed him to easily dominate others making them puppets to his will. He also appeared to be able to telepathically read other beings like the Doctor and monitor progress several thousand miles away with the aid of Osiran computer techology. This included reanimating corpses to use as servants as he did with Marcus Scarman. Sutekh was extremely intelligent and patient.

Behind the scenes
Sutekh's usage of the name Satan is a tricky matter. Many other beings have used the same name or personality, including the Beast, Hades and the Dæmons. It is possible they knew about each other and were in league with each other. Another possibility is that they used the name at different times and didn't come in contact with the others.