Osiris

Osiris was the leader of the Osirans. He ruled Phaester Osiris alongside his brother Sutekh; (PROSE: The Sands of Time) the two of them were specifically bred to channel the energy of Ra. (AUDIO: The Ship of a Billion Years) Isis was Osiris' sister and wife.

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)

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

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)