What was Athena's brother the God of?

Athena has many brothers. Which are all half-brothers because it is believed in ancient Greek mythology that she did not have a mother and was born from Zeus' forehead.

However, Zeus had many affairs and so had many children whom are Athena's half-brothers and half-sisters.

But for the sake, Ares is probably the most known god to be Athena's brother, as well as her opposite, and he is the god of war.