Memnon was an Ethiopian king on the Trojan side in the Trojan War. Achilles killed him in revenge (as Achilles also did with Hector after Patroclus was slain), after Memnon killed Nestor's son Antilochus. Memnon had refused to fight Nestor when challenged by the aggrieved father because the king of Messenia was quite old. Achilles stood in for him, although he had been warned his own death would soon follow Memnon's.
Memnon was the son of the Titan goddess of the dawn, Eos.