Babi was born from the animal that most resembled man. The ancient Egyptians watched the hamadryas baboon, with its dog-like snout, silver-white cape of fur, and crimson hindquarters, and saw not a beast but a deified ancestor. The earliest evidence of his worship comes from the Early Dynastic period, around 3000 BCE, in the form of ivory tags found at Abydos, where the first kings of Egypt were buried. At Tell Ibrahim Awad in the Delta, archaeologists uncovered a faience statue of seven baboons in a single boat, dating to the Second Dynasty, proof that the bull of the baboons was already receiving offerings before the great pyramids were built. The Egyptians called him Babi, a name that meant "bull of the baboons," the alpha male who dominated his troop through sheer aggression and sexual vigour.

In the Pyramid Texts of the Old Kingdom, the oldest religious writings in the world, Babi appears as a power of terrifying potency. The texts describe him as "red of ear and purple of hindquarters," a creature who lived on the entrails of his enemies. But his most famous attribute was his phallus, which the texts call "the bolt of the sky." The double doors of heaven were held shut by great bolts, and it was Babi's phallus that opened them, allowing the deceased king to pass from the earth into the celestial realm. In this role he was the gatekeeper of the west, the direction of the dead, and no soul could ascend without his permission.

As Egyptian ideas of the afterlife grew more elaborate, Babi's role expanded into the Duat, the labyrinthine underworld through which every soul had to travel. In the Coffin Texts of the Middle Kingdom, a collection of spells painted on coffins to protect the dead, Babi becomes the ferryman of the netherworld. Spell 397 declares that his phallus, "which creates children and begets calves," is the mast of the ferry-boat that carries the deceased across the dark waters. Spell 398 goes further, identifying his entire body with the boat itself, while his crew are the netherworld fishermen who cast nets to trap unwary souls. The god Mahaf, the one who looks backwards, leads these fishermen, and the only way for the dead to escape is to know the secret names of every part of Babi's vessel. This knowledge appeased the bloodthirsty god and allowed the soul to slip past his snares.

Babi's virility was not merely a symbol but a practical force in the afterlife. The Egyptians believed that sexual potency was proof that a man was fully alive, even in death. Coffin Text Spell 304 promises the deceased that any woman who comes under its power will make herself available to him for intercourse day and night. In Coffin Text 822, the dead king declares, "I am the phallus of Babi," claiming the god's supernatural potency for himself. In Coffin Text 359, the king goes further, identifying himself as Babi entirely, calling himself the oldest son of Osiris, the green-skinned god of the dead who was murdered by his brother Set and resurrected by his wife Isis. This connection to Osiris made Babi the first-born son of the underworld king, a prince of the Duat with the blood of divinity in his veins.

Yet Babi was also the executioner of the wicked. In the Book of the Dead, the collection of New Kingdom funerary spells that guided souls through the underworld, he stands beside the Lake of Fire, a place of purification and destruction in the Duat. When the heart of the deceased was weighed against the feather of maat, the goddess of truth and cosmic balance, those who failed the test were not merely cast into darkness. Babi devoured them. He fed on their entrails, living on the guts of the unrighteous in a manner that reflected the baboon's own omnivorous and aggressive nature. He was the bloodthirsty guardian who ensured that only the justified reached the Field of Reeds, the paradise of the Egyptian afterlife.

Over the centuries, Babi's worship was gradually absorbed by Thoth, the ibis-headed god of wisdom who was also depicted as a baboon. His cult centre at Khmunu, the city the Greeks called Hermopolis, became Thoth's city. The Papyrus Jumilhac, a mythological text from the Ptolemaic period, records a conflict between Babi and Thoth in which Babi accuses Thoth of theft before the Ennead, the council of nine gods, and the sun god Ra. Thoth retaliates by casting a spell on Babi's phallus, causing it to swell during intercourse so that he becomes trapped with his partner. The Ennead declares Babi guilty, and Thoth executes him on a sacrificial block. The story served to justify the sacrifice of dogs in Thoth's honour, and it marked the symbolic end of Babi's supremacy. Thoth took his city, his baboon form, and his worshippers, leaving Babi as a shadow in the older texts, a ferocious ancestor remembered mainly in spells and coffin paintings.