The birth of Athena
Zeus was the father of Athena and her mother was Metis, which means wisdom. Zeus was told before Athena was born, that any child born to Metis would be more powerful than its father. Zeus was very worried by this and decided to swallow Metis before she could give birth to the child.
Some time later Zeus began to have terrible headaches. The pain grew so unbearable that Zeus asked Hephaistos to cut his head open to see what was wrong.
When Hephaistos opened his head, Athena emerged from Zeus' skull, fully grown and dressed for battle.