The Osirians (also known as Osirans) were a race of powerful and intelligent humanoids.
Physical Characteristics
Osirians, despite their name, look somewhat like depiction of Set. They have grey skin, donkey-like heads with large, square ears and bright green eyes.(DW: Pyramids of Mars) Those of high status in the Osirian Court however are able to change their appearance, adopting a series of different animal heads according to whichever is in fashion (MB: The Ship of A Billion Years). They have expanded brain-cases and a cerebrum like "a spiral staircase", which means they particularity like puzzles. Osirians have advanced psychic powers, including mental projection and telepathy. They can also live for thousands of years, even without sufficient food or water. (DW: Pyramids of Mars)
Technology
Osirians have very advanced, but stylized technology. One common example of Osirian products are the Osirian service robots. They are thin robots with a wire-framework to give them a more humanoid shape and are powered by a cytronic particle accelerator. They had immense strength and could be controlled by a special ring. These robots were wrapped up in specially treated wrappings which gave them the appearances of mummies. Sutekh used several simple Service Robots to do his bidding, while more ornate robots were used on the pyramid of Mars.
Other Osirian technology includes a force field created by generator loops in canopic jars, Time Tunnels embedded in a sarcophagus, a rocket in the shape of a pyramid and technology activated by certain signs. Despite the unusual design, the Osirians are thought to have technology as powerful, if not more powerful, then the Time Lords. (DW: Pyramids of Mars)
History
The Osirian Court exists, like Gallifrey, in a special relationship to the timeline of the wider universe; Its past sometimes overlapping with Gallifrey's future (MB: Coming to Dust). Regardless of the details, the Osirians are evidently an ancient species, having been a major power since at least 150 million BCE. They were involved in the Millennium War in which they were able to stop the creation of a wormhole in the Horsehead Nebula which would have caused massive damage. They were also involved in the final attack against the Mad Mind of Bophemeral. (DW: The Quantum Archangel)
Approximately 7,000 years ago, Phaester Osiris was ruled by Horus and Sutekh. While Horus was a relatively just ruler, Sutekh was a ruthless conqueror who set out to extinguish all life in the universe. He was feared throughout the galaxy and was on the way to even defeat the Time Lords. He also caused the destruction of Phaester Osiris, which wiped out most of the Osirians. The 740 remaining Osirians, led by Horus, were finally able to stop him on Earth. Instead of killing him, they trapped Sutekh in a Egypt, having a pyramid on Mars relay a beam to paralyse him. The defeat of Sutekh led to the creation of Egyptian myths about their gods and their technology influenced the styles of the Egyptians.
By 1911, Sutekh was finally discovered by Marcus Scarman and Sutekh was able to control him. He used Marcus Scarman and several Service Robots to construct a missile, with which he would destroy the pyramid on Mars, freeing him to destroy all life in the universe. (DW: Pyramids of Mars)