In Greek mythology, Deiphobus // (Δηίφοβος Deiphobos) was a son of Priam and Hecuba. He was a prince of Troy, and the greatest of Priam's sons after Hector and Paris. Deiphobus killed four men of fame in the Trojan War.
According to the Iliad (books XII, XIV, XXII), in the Trojan War Deiphobus, along with his brother Helenus, led a group of soldiers at the siege of the newly constructed Argive wall and killed many, and wounded the Achaean hero Meriones. As Hector was fleeing Achilles, Athena took the shape of Deiphobus and goaded Hector to make a stand and fight. Hector, thinking it was his brother, listened and threw his spear at Achilles. When the spear missed, Hector turned around to ask his brother for another spear, but "Deiphobus" had vanished. It was then Hector knew the gods had deceived and forsaken him, and he met his fate at the hand of Achilles.
Some accounts hold that it was Deiphobus and Paris who ambushed and killed Achilles while luring him to their sister Polyxena. After the death of Paris, Deiphobus was given Helen as a bride for his deeds in the war, defeating the bid of his other brother, Helenus. Some accounts say the marriage was by force. When the Trojan Horse was in the city, Deiphobus accompanied Helen as she walked around the horse, calling out the names of the Greeks within in the voices of their wives, because she did not want to look like she was helping them. Menelaus and Odysseus had to hold the men inside back from responding. During the sack of Troy, Deiphobus was slain by either Odysseus or Menelaus, and his body was mutilated. Some accounts say it was Helen who killed him, or that she celebrated his death. Most accounts seem to indicate that, unlike her other two husbands, Helen didn't love Deiphobus and decided she would rather return to Menelaus.
In Virgil's Aeneid, Deiphobus, horribly mutilated during the sack of Troy, appears to Aeneas in the Underworld. He tells him the story of his death, which entails Helen's betrayal in signaling Menelaus to Deiphobus's bedchamber. While with Aeneas, he begs the gods for revenge against the Greeks.
One modern account, The Luck of Troy by Roger Lancelyn Green, depicts him as a particularly unpleasant character.