Castor and Pollux,
in Greek and Roman mythology, the twin sons of Leda, wife of the Spartan king Tyndareus. They were the brothers of Clytemnestra, queen of Mycenae, and Helen of Troy. Although both boys were known as the Dioscuri, or Sons of Zeus, in most accounts only Pollux was held to be immortal, having been conceived when Zeus appeared to Leda in the form of a swan. Castor, his fraternal twin, was considered the mortal son of Tyndareus. Both were worshiped as deities in the Roman world, however, and were regarded as the special protectors of sailors and warriors. Living just before the Trojan War, the brothers took part in many of the famous events of the day, including the Calydonian boar hunt, the expedition of the Argonauts, and the rescue of their sister Helen when she was carried off by the Greek hero Theseus. Throughout their adventures the brothers were inseparable, and when Castor was slain by Idas, a cattle owner, in a dispute about his oxen, Pollux was inconsolable. In response to his prayers for death for himself or immortality for his brother, Zeus reunited the brothers, allowing them to be together always, half the time in the underworld and half with the gods on Mount Olympus. According to a later legend, Castor and Pollux were transformed by Zeus into the constellation Gemini, or The Twins.