Osiris

Osiris was the last great leader of the Osirans of Phaester Osiris, venerated in Egypt, on Earth, as one of their most important gods. He was murdered by his destructive fellow Osiran Sutekh, and his murder avenged by his son Horus — both facts recorded in the Egyptian myths.

Rule
Osiris ruled Phaester Osiris alongside Sutekh; though Sutekh was his brother, (PROSE: The Sands of Time) the Legend of Sutekh claimed that Osiris had been Sutekh's father, instead. (PROSE: Background) Sutekh and Osiris had been specifically bred to channel the energy of Ra. (AUDIO: The Ship of a Billion Years) Isis was Osiris' sister and wife. (PROSE: The Sands of Time)

Murder by Sutekh
Sutekh grew jealous of Osiris's power over the Court, deeming that, as he, Sutekh, was responsible for its continued survival, he should be far more respected by the other Osirians than Osiris himself. (AUDIO: Coming to Dust, The Ship of a Billion Years)

Sutekh, having decided to kill his brother, lured Osiris into a space capsule. Sutekh and his sister/wife Nephthys were able to propel the capsule into space and stop Osiris from mentally projecting himself. He suffocated in the vacuum of space and was unable to project his mind over the great distances. While Isis was searching for him, he was eventually able to project part of his mind into the pilot of her ship, giving birth to his psi-child Horus. (PROSE: The Sands of Time)

According to a different if comparable account, Sutekh, not managing to snuff Osiris out entirely, killed his body and buried it on Earth, with Osiris's mind still aware as his body decayed and separated into its constituent strands of biodata. Learning of this, the Faction Paradox Cousins Eliza and Justine decided to thwart Sutekh's claim to the throne by resurrecting Osiris. They collected all the samples they could of Osiris's biodata and brought them to Anubis, the most killed Osirian flesh-sculptor, so that he could reconstitute a body for Osiris. Because they were missing some key elements, however, Eliza had to give herself up as a donour, merging with the surviving essence of Osiris to become Horus, (AUDIO: Body Politic) who subsequently fought and defeated Sutekh at the cost of his own resurrected life. (AUDIO: Words from Nine Divinities, The Judgment of Sutekh)

The Legend of Sutekh claimed that Sutekh's punishment, once Osiris's son Horus caught up with him, was to forever bear the body of Osiris on his shoulders; (PROSE: Background) the Fourth Doctor would later discovere that Horus had trapped Sutekh in eternal paralysis beneath a pyramid, a type of tomb. (TV: Pyramids of Mars)

Return
However, Osiris returned to Earth years later in the hopes of recapturing it. (COMIC: Spiral Staircase)

Legacy
While battling Vlad the Impaler's soldiers in Wallachia on 17 June 1462, Erimem swore by Osiris. (AUDIO: Son of the Dragon)

While confronting the vampire Joanna Harris, the Eighth Doctor implied that Osiris had been one of his past identities; James Court (who witnessed said confrontation) thought this to have been a joke but couldn't be sure. (PROSE: Vampire Science)

In human culture
A market in 1st century Byzantium had a temple to Isis and Osiris at its entrance. (PROSE: Byzantium!)

While pretending to be a faith healer in order to be allowed to treat Colin McLaren's wounds, the Second Doctor mentioned Isis and Osiris and various astrological terms. (TV: The Highlanders)

Personality
Osiris was viewed as unbearably compassionate by Sutekh, who compared his generous views of all other lifeforms to the Fourth Doctor's. (TV: Pyramids of Mars) During his reign, he turned the Osirians to the purpose of civilising "lesser species", finding primitive, barbaic societies and raising them to great levels of technology and cultural refinement, albeit at the cost of becoming slaves to their Osiran gods. Although certainly more benevolent than Sutekh, his imperialist tendencies meant he was viewed with a degree of suspicion by humans such as Justine. (AUDIO: Coming to Dust, The Ship of a Billion Years) After merging with Osiris to become Horus, the Eliza half of Horus spoke with dismay of how little Osiris seemed to care for the lives of individual mortals, including herself. (AUDIO: The Judgment of Sutekh)