In the beginning of time, Zeus, the supreme god of Olympus consolidated himself as the supreme lord of the universe but before he had the goddess Hera as his queen, Zeus had another wife. There was a goddess as beautiful as she was wise, her name was Metis-daughter of the titan Oceanus, who helped Zeus free his siblings form the belly of their Father Kronos. Zeus was fascinated by the precious deity and wanted to take her as his wife, but the goddess resisted his approaches. Metis tried to escape from the god in every way, but Zeus was persistent. The goddess had the power of metamorphosis and could transform herself into anything and so she used this power to escape Zeus, but Metis could not escape Zeus forever. The god set an ambush for the disguised goddess. The lord of thunder jumped on Metis and grabbed her and so Metis was trapped and could not Escape Zeus's strong arms and finally submitted to his will.
With the cunning goddess at his side, the reign of Zeus seemed more prosperous, and the gods became able to deal with all the chaos that had existed in the world since primordial times. However, during a visit to Gaia-the primordial goddess that personifies the earth, she revealed a terrible omen. Gaia told Zeus that his wife would have 2 children. The first would be a girl who would equal the strength and wisdom of her father but the second would be a boy who would become stronger than his father and would take away his power. Zeus feared having the same outcome as his father-the titan Kronos, or his grandfather-the god Uranus, as both had been dethroned by their sons.
However, Zeus, inspired by his father devised a plan to prevent the omen from coming true. Zeus asked Metis to transform herself into a drop of water so she could give him a taste of her metamorphic power and so Zeus swallowed his wife so that she could not give birth to the being that would dethrone him. After swallowing his wife, Zeus incorporated the powers of the goddess Metis, and he became a much wiser, fairer and less impulsive god but he didn't know that she was already pregnant. So as time passed Zeus began to feel terrible headaches, he felt a horrible pain that felt like his head was going to explode.
So, Zeus asked for his head to be opened and the source of the pain removed because could no-longer withstand such pain and so the Titan Prometheus struck the god on the head with an axe and a strong light began to emerge from the open crack in Zeus's head and a female figure surfaced on Zeus's head and from Zeus's forehead emerged the goddess Athena along with her armor and weapons fully grown to fit her. Zeus was proud to give birth to that formidable creature and with her mother's intelligence, Athena would become the goddess of wisdom, she was also considered the goddess of defensive warfare and therefore confrontations against Ares-the god of war would be inevitable.
As for Metis, she remained in Zeus's stomach and so the prophecy of the second child was never fulfilled. Athena proved herself to be a brave, pure, just and wise goddess, She was considered the favorite daughter of Zeus and was thought by many that she was Zeus's legitimate Successor.