Horus

Horus was brother (or nephew) to fellow Osirian Sutekh.

Birth(s)
Sutekh, who was also brother to Osiris, ruled Phaester Osiris. When Sutekh killed Osiris, he projected his mind into a pilot of an Osirian ship, 'birthing' a psi-child who (probably) led to Horus. (MA: The Sands of Time)

Horus was birthed after Sutekh killed Osiris and buried his corpse underneath a cache of Faction Paradox reproductive technology. The technology was damaged and reacted with Osiris' biomass creating fractured and partial forms, though these forms led to Horus' birthing. (MB: The Ship of a Billion Years)


 * The latter of these accounts occurs following the former if viewed through a linear timeline, however it is suggested that the latter occurred first; see Osirians for more information.

Rise and Leadership
After Osiris' death, Sutekh and Nephthys both escaped to Earth, destroying Phaester Osiris. The 740 remaining Osirians 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 tortuous. (DW: Pyramids of Mars, MA: The Sands of Time)

Worship
Horus was later, following his death, worshipped by many cultures. The Egyptians of Earth worshipped him amongst the pantheon of gods, many of whom were named after or were Osirians.

The native Martians also worshipped 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. (NA: GodEngine)