Hera had him without a partner because she wanted to get even with Zeus for having a child without her(he had a child living in his thigh b/c the mother died)
Zeus disliked Ares. Once Ares went missing a few years because he was abducted by the giant Aloadai twins and was kept in a bronze Jar and Zeus didn't go looking for him. Hermes was the one who let him out of the jar.
In the Trojan War Ares sided with Aphrodite and fought for Hector up until Athena guided a Greek warrior's arrow to pierce Ares. Ares then departed the battlefield to complain to Zeus about Athena's violence