Athena was the goddess of wisdome and miltary victory, and also the patron of the city of Athens, she was also Hercules' half sister. She was the daughter of Zues and Metis. There was a prophecy that the child of born by from Metis would overthrow Zues and become the next ruler of heaven. So to prevent that Zues swallowed Metis while she was still pregnant to prevent the prophecy to ever happen. But Zues later on developed a headache and begged Hephaestus to open his head to get rid of his headaches. When he opened he opened his head out spung Athena fully grown and ready for battle.
Sources: http://www.perseus.tufts.edu/Herakles/athena.html
http://paleothea.com/SortaSingles/Athena.html
