Ajax (Greek: Aîas), a Greek hero, son of Oileus the king of Locris, called the "lesser" or Locrian Ajax, to distinguish him from Ajax, son of Telamon. He was the leader of the Locrian contingent during the Trojan War. He is a significant figure in the Iliad and is mentioned in the Odyssey.

Homer gives a favorable description of him as a warrior. In spite of his small stature, he held his own amongst the other heroes before Troy; he was brave, next to Achilles in swiftness of foot and famous for throwing the spear. But he was boastful, arrogant and quarrelsome; like the Telamonian Ajax, he was the enemy of Odysseus, and in the end the victim of the vengeance of Poseidon, who wrecked his ship on his homeward voyage (Odyssey, iv. 499).

A later story gives a more definite account of the offense of which he was guilty. It is said that, after the fall of Troy, he dragged Cassandra away by force from the statue of the goddess at which she had taken refuge as a suppliant, and raped her (Lycophron, 360, Quintus Smyrnaeus xiii. 422). For this, his ship was wrecked in a storm on the coast of Euboea, and he himself was struck by lightning (Virgil, Aeneid I. 40).

He was said to have lived after his death in the island of Leuke. He was worshipped as a national hero by the Opuntian Locrians (on whose coins he appears), who always left a vacant place for him in the ranks of their army when drawn up in battle array. He was the subject of a lost tragedy by Sophocles. The rape of Cassandra by Ajax was frequently represented in Greek works of art, for instance on the chest of Cypselus described by Pausanias (v. 17) and in extant works.

Ajax the lesser was the father of Eurysaces by Tecmessa.