In Greek mythology, Leucus (Leukos) is the Cretan foster son (or associate) of King Idomeneus who, during the Trojan War, becomes Meda's lover, kills the queen and her children, seizes much of Crete, and drives Idomeneus into exile on his return — the island parallel to Aegisthus at Mycenae. Distinct from Homer's companion of Odysseus slain by Antiphus.
Adapted from Wikipedia, "Leucus" · CC BY-SA 4.0
I.Usurper of Crete
Apollodorus' Epitome and the Lycophron scholia tell how Nauplius, wrecking heroes' homes while they fought at Troy, corrupts Meda, wife of Idomeneus. She takes Leucus as lover; he then murders Meda and her daughter Cleisithyra (betrothed to him) and Meda's sons, and detaches ten Cretan cities.
When Idomeneus returns victorious from Troy, Leucus drives him from the island. The tale pairs Crete with the adulterous returns of Agamemnon and Diomedes.
II.Homonyms
Homer names a Leucus among Odysseus' men, killed by Antiphus. Nonnus knows a Lesbian singer in Dionysus' army; Hermes bears the epithet Leucus in Boeotia.
The atlas id leucus-crete is solely the Idomeneid usurper of the Returns tradition.