This is one of the most famous 'birth' stories in ancient Greek mythology. The goddess Athena was, literally, Zeus' 'brainchild'.

Zeus had an affair with Metis, the goddess of intelligence. When she inconveniently became pregnant, he turned her into a fly and swallowed her. Nine months later he had an horrendous migraine.... Zeus called on his son Hephaistos to come and cut his head open with an axe. Hephaistos duly obeyed and out popped baby Athena, fully armed and ready for action!