This is the alternate name for Diomedes, a character in The Iliad. He is the son of Tydeus, and the king of Argos. He fought on the side of Greeks.
He was a feared and respected warrior during the Trojan War, and almost killed Hector, the son of Priam by hitting him in the head with a spear. However, his helmet deflected the blow, and Hector lived to ravage the Greek ranks until Achilles killed him.
Diomed created an interesting contrast to Odysseus. During the Trojan War, Diomed wounded both Ares and Aphrodite with his spear, and yet he returned safely home to Argos following the war. Odysseus on the other hand, forgot to sacrifice to the gods after the war. As punishment, he was doomed to wander the world completely alone for twenty years, longing for is home Ithaca, and his wife, Penelope.
So the moral of the story seems to be that if you are angry, feel free to attack the gods; but you better sacrifice a few sheep afterwards.