Lynceus was born into the royal family of Messenia. His father was Aphareus, son of Perieres and Gorgophone, daughter of Perseus. His mother was Arene, daughter of Oebalus, though later writers also named Polydora or Laocoosa. His brothers were Idas and Peisus. Some traditions made Idas the son of Poseidon rather than Aphareus, but the brothers grew up together in the same Messenian household and were inseparable in war, sport and rivalry. The family held authority around Arene, a city of the western Peloponnese, and was bound by kinship to Leucippus, father of Hilaeira and Phoebe, the daughters later called the Leucippides.

His name gave him his defining trait. Lynceus could mean Lynx-like or Lynx-eyed, and Greek writers treated his sight as almost supernatural. Apollonius of Rhodes describes him as excelling in keenness of vision if the report was true: he could direct his sight even beneath the earth. Apollodorus sharpens the claim, saying that Lynceus could see things underground, through walls, trees and solid matter. Later tradition made his eyes powerful enough to see through darkness and to distinguish objects many miles away. His sight was not merely sharp. It penetrated what others could not perceive.

Lynceus joined Jason and the Argonauts when they sailed from Iolcus to Colchis in search of the Golden Fleece. Apollonius names him among the heroes from Arene, brother of proud Idas, and gives him the role of lookout. On a voyage filled with monsters, rocks, clashing seas and strange peoples, the man who could see underground and through obstacles had an obvious place aboard the ship. He stood in the rigging or prow and scanned what the others could not yet distinguish. The poem does not grant him many independent actions, but his function is essential. Every Argonautic voyage needed eyes before it needed swords.

He was also counted among the hunters of the Calydonian Boar. When Artemis sent the monstrous beast to ravage Calydon because King Oeneus had omitted her sacrifice, heroes from across Greece gathered to hunt it. Meleager, son of Oeneus and Althaea, led them. Atalanta, the swift huntress of Arcadia, joined the expedition, as did Peleus, Telamon, Theseus, Admetus and many others. Lynceus stood among the company with Idas. The hunt tested archery, spear-work, courage and judgement, and the division of the boar's skin afterwards helped ignite the quarrel that destroyed Meleager's household. Lynceus survived the hunt and returned to Messenia with his reputation intact.

His greatest conflict began with the daughters of Leucippus. Leucippus, brother of Aphareus and Tyndareus, had two beautiful daughters: Hilaeira and Phoebe. Hilaeira was promised to Lynceus and Phoebe to Idas. The sisters were priestesses, Hilaeira of Artemis and Phoebe of Athena, and their marriages would have joined two branches of the Messenian royal family. The Dioscuri, Castor and Pollux, sons of Leda and Tyndareus or Leda and Zeus, desired the sisters and carried them away from Messenia. In some tellings they took the women on their wedding day. In others they seized them from the palace and brought them to Sparta, marrying them against the wishes of their betrothed cousins.

The theft placed two pairs of brothers on a collision course. Lynceus and Idas were cousins, rivals and former companions of the Dioscuri. Castor and Pollux were Spartan princes, famous horsemen, boxers and sons favoured by Zeus. Their seizure of the Leucippides violated the promised marriages and the authority of Leucippus. The Apharetidae answered with force. The feud was not limited to the abduction. Pindar's account joins it to a cattle raid in which the Dioscuri drove off a herd belonging to the sons of Aphareus and then ambushed them. Idas tricked the twins with a division of the spoils and warned them not to attempt reprisal. The conflict became both romantic and political, a feud of brides, cattle and kingship.

The final battle turned upon Lynceus' sight. The Dioscuri hid inside a hollow oak tree, thinking themselves concealed. From the height of Mount Taygetus or the surrounding country, Lynceus looked down and saw through the bark and wood into the hidden interior. His eyes discovered what Zeus, Tyndareus or the Spartan landscape had concealed. He told Idas where the twins waited. Idas drove his spear through the hollow oak and killed Castor. The mortal Dioscurus fell, and the balance of divine and human power broke.

Pollux rushed to avenge his brother. In the fighting that followed, Lynceus threw a rock and wounded Pollux, but the immortal son of Zeus struck him down. Idas then attacked Pollux in fury. Zeus intervened with a thunderbolt, killing Idas before he could destroy his immortal son. In the most familiar version, Pollux begged Zeus to restore Castor or share his own immortality with him. The twins became the constellation Gemini, spending alternate days beneath the earth and in heaven. Lynceus died with Idas, the mortal half of a mortal pair.

The deaths of the brothers gave the feud its final symmetry. Two brothers from Messenia opposed two brothers from Sparta. Both pairs had divided paternity, divided mortality and divided claims to the same women. Castor and Lynceus fell, Idas and Pollux survived long enough to exchange blows, and Zeus destroyed the last aggressor. The women at the centre of the feud, Hilaeira and Phoebe, were carried into Sparta and eventually honoured there as divine figures. Their cult joined the memory of the abduction to the memory of their divine husbands. Lynceus became the bridegroom who lost his bride and then his life.

Pausanias preserves the Spartan side of the story. At Sparta the Leucippides had a sanctuary where Hilaeira was connected with Athena and Phoebe with Artemis. At Therapne they appeared within the sacred landscape of Helen and Menelaus, transformed from abducted Messenian women into honoured Spartan cult figures. The Apharetidae did not receive a comparable cult at Sparta. Their role was the necessary darkness that made the Dioscuri shine.

Ancient art repeatedly showed the abduction and the combat. A metope from the Treasury of the Sicyonians at Delphi shows the Dioscuri and the Apharetidae around the cattle. Athenian red-figure vases show Castor and Pollux carrying away the Leucippides while Lynceus and Idas pursue or fight. Roman sarcophagi use the scene of the abduction as an image of beauty, violence and the rivalry of brothers. The hollow oak became especially important in later retellings because it turned Lynceus' sight into the trigger of the catastrophe. The man who could see everything discovered the one thing that made war inevitable.

His eyes gave the ancient world a proverb. Lynx-eyed became a phrase for exceptional perception, and Lynceus became the mythical embodiment of the power. Yet his story also carries a warning. His sight found the Dioscuri, but his sight could not save him. Knowledge penetrated concealment without mastering consequence. Once Lynceus saw through the oak, Idas could strike; once Castor fell, Zeus had to intervene; once Zeus intervened, Lynceus was doomed.

The two Lynceuses were sometimes confused because their stories share sharpness, marriage and violent transformation, but they belong to different cycles. The Lynceus of this record is the son of Aphareus, brother of Idas, Argonaut, hunter and opponent of Castor and Pollux. He is not the son of Aegyptus who married Hypermnestra and became king of Argos. The distinction matters. One Lynceus belongs to the Peloponnesian feud of the Dioscuri; the other belongs to the Danaid tragedy of mass marriage and survival.