The Cult of Isis is ostensibly an offshoot of the Cult of Thoth, founded when Isis turned away from the search for Ascension to help her brother-husband Osiris and son Horus in their struggle against Set. The members of the Cult pledge their loyalty to Ma'at, the principle of virtue and order, and in return learn the secret of Ra-Hekau or true magic.
The cult's fortunes have risen and fallen numerous times during its long history. Horus installed the cult in the priesthood of nearly every temple in Egypt, but by the eve of the Roman occupation they had degenerated into listless hedonists and even permitted a version of the Spell of Life to fall into the Setites' hands. Under the Romans, the cult underwent a revival, but also fragmented into numerous autonomous mystery cults. Factions of the cult are now found among several Traditions, including House Shaea of the Order of Hermes, the Celestial Chorus, Verbena, and the Cult of Ecstasy. Some continue to look to Horus for guidance, but others chafe under his rule. Most continue the struggle against the Followers of Set.