To the ancient Egyptians the sun was not a fixed fact but a daily achievement, and Ra (also written Re) was the god who accomplished it. He is the creator and sustainer, self-generated at the first moment on the primeval mound, whose light brings the ordered world into being each dawn. Egyptian theology gave the sun distinct forms across the day: Khepri, the scarab, at the morning rising; Ra at the full noon; and Atum, the aged god, at the setting, one deity in three phases of a single journey.
That journey was the heart of the cult. Ra sails across the sky by day in the solar barque, then passes at night through the Duat, the underworld, where he must be renewed. Each night he confronts Apep (Apophis), the serpent of chaos, who tries to swallow the sun and halt creation; the god's victory before dawn is not guaranteed but won, again, every night. Egyptians understood the ritual maintenance of the temples as their share in keeping that victory possible.
His principal cult centre was Heliopolis (Egyptian Iunu), whose priesthood placed Ra at the head of a group of nine creator-gods, the Ennead.