Lynceus was the jealous murderer of Castor, along with his brother, Idas

Idas

In Greek mythology, Idas was a son of Aphareus and Arene and brother of Lynceus. He and Lynceus loved Hilaeira and Phoebe and fought with their rival suitors, Castor and Polydeuces, killing the mortal brother Castor. He was also one of the Argonauts and a participant in the hunt for the Calydonian...

. Idas and Lynceus murdered Castor because they all (along with Polydeuces

Polydeuces

Polydeuces may refer to:*Polydeuces , a moon of Saturn*An alternative name for the Greek mythological hero Pollux...

) sought Phoebe and Hilaeira

Hilaeira

In Greek mythology, Hilaeira was a daughter of Leucippus and Philodice. She and her sister Phoebe are commonly referred to as Leucippides ....

, daughters of Leucippus

Leucippus

Leucippus or Leukippos was one of the earliest Greeks to develop the theory of atomism — the idea that everything is composed entirely of various imperishable, indivisible elements called atoms — which was elaborated in greater detail by his pupil and successor, Democritus...

 (who was also Idas and Lynceus' uncle in some versions). Lynceus was one of the Argonauts

Argonauts

The Argonauts ) were a band of heroes in Greek mythology who, in the years before the Trojan War, accompanied Jason to Colchis in his quest to find the Golden Fleece. Their name comes from their ship, the Argo, which was named after its builder, Argus. "Argonauts", therefore, literally means...

 and he participated in the hunt for the Calydonian Boar

Calydonian Boar

The Calydonian Boar is one of the monsters of Greek mythology that had to be overcome by heroes of the Olympian age. Sent by Artemis to ravage the region of Calydon in Aetolia because its king failed to honor her in his rites to the gods, it was killed in the Calydonian Hunt, in which many male...

. He was a son of Aphareus

Aphareus

In Greek mythology, Aphareus , son of Gorgophone and Perieres, was the husband of Arene, daughter of Oebalus, and father of Lynceus, Idas and Peisus, though some report that Idas' actual father was Poseidon. Some call his wife Polydora or Laocoosa...

 and Arene and was said to have excellent sight, even able to see through trees, walls and underground.