Metis Titan-Goddess

Metis was one of the Titans, a daughter of Oceanus and Tethys; therefore, she was considered an Oceanid.

Metis and Zeus
She was the first wife of Zeus, and became the goddess of wisdom, prudence and deep thought. According to a prophecy, Metis would bear two children, the first being Athena, while the second one, a son, would be so powerful that would overthrow Zeus. Zeus, afraid of this, tricked Metis into turning herself into a fly, and swallowed her.

However, Metis was already pregnant to Athena, and, inside Zeus' stomach, she started creating a helmet for her daughter. Zeus was in such pain that he asked Hephaestus to hit his head with an axe; as soon as his head was opened, Athena jumped out fully grown and clad in armour.

Athena's Mother
It is often said that Athena had no mother and she was born out of Zeus alone; this doesn't necessarily conflict with this account, as the ancient Greeks believed that children were descendants of the fathers, while mothers did not contribute to the creation of their children.