Deiphobus is a Trojan warrior who is one of the many sons of Priam. In Iliad 22, Homer describes him as a "tireless speaker" (Kline translation).
Deiphobus' most significant appearance in Homer's Iliad occurs in a passage in which he does not actually appear at all. In Iliad 22, Achilles is chasing Hector around the walls of Troy. Hector realizes that he is no match for Achilles by himself, but when he sees Deiphobus, he thinks that together they can face Achilles. Unfortunately for Hector, this Deiphobus is actually the goddess Athena, who has taken on the form of Deiphobus in order to trick Hector into stopping. Soon after Hector stops, Deiphobus vanishes.
Other ancient sources outside of Homer say that Deiphobus and Paris/Alexander managed to assassinate Achilles (see Dictys of Crete 4.11).
Other sources also tell us that after Paris died, Deiphobus married Helen, albeit temporarily since Deiphobus was killed during the fall of Troy.