Zeus first was was Metis, a titan. He became obsessed with her, even though she ran away and resented him, by changing into different forms such as birds or fish. Although Zeus was also capable of this and eventually, she gave in and the two got married.
Metis became pregnant with a child, but great oracles told that the child would be very powerful and able to verthrow Zeus, much like himself to his father. Zeus took this warning very seriously.
your child is going to be very powerful.
When he next saw Metis, he initially flattered her and put her at her ease. Then, with Metis' guards down, Zeus opened his mouth and swallowed her and her unborn child. This caused Zeus much distress. Zeus decided that the only way to intervene this from happening would be to stop metis having the child.
After a time, Zeus developed an unbearable headache, which made him scream out of pain so loudly it could be heard throughout the earth. The other gods came to see what the problem was. Hermes realized what needed to be done and directed Hephaestus to take a wedge and split open Zeus's skull.
Out of the skull sprang Athena, fully grown and in a full set of armour. Due to the way of her birth, she became the goddess of intelligence and wisdom.