In Egyptian mythology, the giant serpent of chaos that opposes Ra is Apep.
Apep, also called Apophis, represents chaos, darkness, and disorder, standing against Ra’s solar journey and the principle of ma’at—cosmic order, balance, and truth. Each night, Ra’s solar barque was believed to travel through the underworld, where Apep tried to halt the sunrise by attacking or swallowing the sun.
Egyptian artists usually portrayed Apep as an enormous serpent. Some accounts describe him as living in the Duat, the underworld, and explain eclipses, storms, or other disturbances as manifestations of his struggle with the sun god. Priests performed protective rituals and recited spells intended to restrain, bind, or destroy the serpent symbolically.
A common mix-up is the name: Apep is the Egyptian form, while Apophis is the Greek rendering. Nehebkau was another major serpent in Egyptian mythology, but he was associated with protection and the underworld rather than serving as Ra’s principal enemy. In some traditions, Set helps Ra repel Apep.