In Greek mythology, Glaucus was a Lycian captain under his cousin Sarpedon in the Trojan War. Grandson of Bellerophon through Hippolochus, he is best known for the guest-friendship scene in Iliad Book 6 in which he and Diomedes exchange armour — golden for bronze — after discovering their grandfathers' friendship. He fights through the wall assault and the struggle over Sarpedon's body; later epic has Ajax kill him over Achilles' corpse, after which Apollo bears him home to Lycia.
Adapted from Wikipedia, "Glaucus (son of Hippolochus)" · CC BY-SA 4.0
I.Family and the armour exchange
Glaucus was son of Hippolochus and grandson of Bellerophon, of the Corinthian line settled in Lycia. Malalas describes him as strong, sensible, and pious. In Iliad Book 6 he meets Diomedes between the hosts; asked his lineage, he recounts Bellerophon's line and Hippolochus' charge never to shame his fathers. Diomedes recalls that his grandfather Oeneus had hosted Bellerophon; they declare guest-friendship, clasp hands, and exchange armour — but Zeus takes Glaucus' wits so that he gives golden armour worth a hundred oxen for Diomedes' bronze worth nine.
II.War and death
With Sarpedon and Asteropaios he fights in the division that helps Hector breach the Achaean wall; Teucer wounds his arm with an arrow and forces him back. When Sarpedon falls, Glaucus prays to Apollo, who heals the wound so he can rally the Trojans around the body until the gods remove it. In Quintus of Smyrna's Posthomerica, fighting over Achilles' corpse, Ajax kills him; Aeneas rescues the body and Apollo carries it to Lycia, where nymphs raise a spring still called after him.
This notice concerns the Lycian son of Hippolochus — not Glaucus of Corinth (Bellerophon's father), the sea-god Glaucus, or other Homeric namesakes.