Set is Hoor-paar-kraat, the 'secret seed', released from the egg by the shattering force of the lightning flash of illumination. Hoor-paar-kraat is the unmanifest twin of Ra-Hoor-Khuit (Horus the Child). This is the Hidden God of the Egyptian Book of the Dead, the Sun in Amenti.
Within Thelema, Ra-Hoor-Khuit is called the Lord of the Aeon (which began in 1904 according to Thelemic doctrine), and The Crowned and Conquering Child. "Now let it be first understood that I am a god of War and of Vengeance." AL III:3
Aiwass, the being who dictated The Book of the Law to Crowley, introduces himself as "the minister of Hoor-paar-kraat" in the book's first chapter.