Sutekh, who was also brother to Osiris, ruled Phaester Osiris. When Sutekh killed Osiris, he projected his mind into a pilot of an Osiran ship, "birthing" a psi-child who (probably) led to Horus. (PROSE: The Sands of Time)
Rise and leadership
After Osiris' death, Sutekh and Nephthys both escaped to Earth, destroying Phaester Osiris. The 740 remaining Osirans were led by Horus in battle against Sutekh, finally defeating him in Egypt. Feeling that they could not stoop to Sutekh's level by killing him, they trapped Sutekh in Egypt, having a pyramid on Mars relay a beam to paralyse him, stopping him from moving or projecting his mind. They also set the methods to free himself just out of his reach in order to make the punishment that much more torturous. (TV: Pyramids of Mars, PROSE: The Sands of Time)
In the 16th century, the cryogenic systems failed and Horus actually died.
The native Martians also worshiped Horus. Forming the Holy Order of Oras, they followed the teachings of the Book of Oras. The Order's teachings were of a non-violent nature and asked its followers to abandon such means. The Ninth Book of Oras was the Rebirth of the Father. (PROSE: GodEngine)