Metis
When she was inside Zeus, Metis made a helmet and a robe for her baby. The hammering noise caused Zeus to have a headache. To try and help Zeus with the pain, Prometheus, Hephaestus, Hermes, or Palaemon (depending on the myth) cut his head open with a Minoan axe.  Athena then came out of Zeus's head. She was fully grown and had her armour on.