Once upon a time, Zeus, the mighty son of the lovely-haired Rhea, became the overlord of the universe. Metis, the daughter of Okeanos and Tethys, had helped Zeus by preparing a vomitive for Kronos, due to which Zeus was united with his siblings. Metis had also helped Zeus with her astute counsel, during the Titanomachy.
Zeus loved and desired his first love, the fair-cheeked Metis. Initially, Metis tried to withdraw from Zeus, but later, she yielded and they got married. Gaia and Ouranos prophesied that Metis shall bear very wise children. First, a bright-eyed maiden Tritogeneia shall be born, who shall be equal to Zeus in understanding and strength. Next, a son of overbearing spirit shall be born, who shall become the king of gods and men. This prophecy troubled Zeus, as it foretold that his royal sway over the eternal gods, might be taken away by the children of Metis.
Hence, acting on the advice of Gaia and Ouranos, Zeus used slippery speeches and treachery, to deceive the fair-faced Metis. Zeus wholly swallowed Metis into his own belly, so that Metis would have no children, but would still be able to counsel him. However, Metis had already conceived the gray-eyed Athene in her womb. Remaining hidden in the inward parts of Zeus, Metis delivered the war-like Athene, who grew as time passed. Metis, the wise worker of right actions, gave Athene the strength that excelled all the other immortals, a most excellent enemy-scaring armor, and weapons of war.
As a result, Zeus suffered a terrible headache. On the bank of the river Trito, Prometheus, the son of the Titan Iapetus and Oceanid Klymene, took hold of a two-headed axe and cleaved the head of Zeus. From the cleaved head of Zeus, out leapt forth the fully grown bright-eyed Athene, resplendent in a shining armor, arrayed with arms of war, and shouting a terrible war-cry. The heavens resounded with the birth of the flashing-eyed Tritogeneia.
Excerpt from the book “Once Upon A Time-II: 150 Greek Mythology Stories” by Rajen Jani