In Greek mythology, Oeax or Oiax (Ancient Greek: Οἴαξ, "tiller" or "rudder-handle") was a Euboean prince, son of King Nauplius and brother of Palamedes and Nausimedon. After Odysseus engineered Palamedes's death at Troy, Oeax avenged his brother — notably by lying to Clytemnestra that Agamemnon was bringing Cassandra home as a concubine — and was later killed by Pylades while aiding Aegisthus.
Adapted from Wikipedia, "Oeax (mythology)" · CC BY-SA 4.0
I.Family
Oeax was son of Nauplius the Wrecker. His mother is variously Clymene (daughter of Catreus), Hesione, or Philyra. His brothers were Palamedes, the inventive counsellor at Troy, and Nausimedon.
II.Troy and vengeance
Oeax accompanied Palamedes to Troy. When Odysseus's treachery led to Palamedes's death, Euripides's lost Palamedes has Oeax carve the news on oar-blades and cast them into the sea so that Nauplius might learn of it; Nauplius then came to the Greek camp demanding justice and left empty-handed. One tradition says the Greeks tried to throw Oeax into the sea and Nereids rescued him.
Angry at the Greeks, Oeax falsely told Clytemnestra that Agamemnon was bringing home the Trojan princess Cassandra as a concubine — the slander that sharpened her plot with Aegisthus. He later tried to have Orestes banished after the matricide. Helping Aegisthus against Orestes, Oeax and Nausimedon were killed by Pylades.