In Greek mythology, Lynceus was a descendant of Belus through Aegyptus, twin brother of Danaus, who had fifty daughters, the Danaides, while Aegyptus had fifty sons including Lynceus. Aegyptus commanded that his sons marry the Danaides and Danaus fled to Argos, ruled by King Pelasgus with his daughters. When Aegyptus and his sons arrived to take the Danaides, Danaus gave them to spare the Argives the pain of a battle.

Lynceus (in Greek, Lynkeus) was the jealous murderer of Castor, along with his brother, Idas. Idas and Lynceus murdered Castor because they all (along with Polydeuces) sought Phoebe and Hilaeira, daughters of Leucippus (who was also Idas and Lynceus' uncle in some versions). Lynceus was one of the Argonauts and he participated in the hunt for the Calydonian Boar.