The serpent god who protected the pharaoh and was associated with the underworld was Nehebkau.
Nehebkau was an ancient Egyptian serpent deity whose name is commonly interpreted as “he who harnesses the kas,” referring to the spiritual forces or life-essences of an individual. His protective role extended to the deceased king, whom he could guard, nourish, and assist in the afterlife.
Egyptian tradition gave Nehebkau an ambivalent early character. Older accounts could portray him as a dangerous, primordial serpent, but later religious texts present him as a powerful and benevolent guardian. He became associated with Ra and with the Court of Maat, where the dead were judged after death. He was also described as guarding the gates or pathways of the underworld.
Nehebkau is often shown as a full serpent, a serpent with human limbs, or a human figure with a snake’s head. He is easy to confuse with Wadjet, the cobra goddess and royal protector of Lower Egypt; Mehen, the serpent who coils around and protects Ra’s solar barque; and Apophis, the hostile chaos serpent.