Castor and Pollux, in Greek and Roman legend, sons of the Spartan queen Leda. One legend says they were twins, and that Zeus was their father. According to another legend, Zeus was the father of Pollux, and Tyndareus, king of Sparta, was the father of Castor. The beautiful Helen of Troy and Clytemnestra, the wife of Agamemnon, were their sisters.

Castor and Pollux were close companions and shared many adventures. They were heroes of the Argo expedition. While the Argonauts were at sea, a terrible storm arose, and all hands called upon the gods for mercy. Suddenly twin stars appeared above the heads of Castor and Pollux, and the storm died. From that time on, the brothers were regarded as special guardians of seamen.

After the Argo expedition, according to some accounts, the brothers kidnapped the brides of their cousins, Idas and Lynceus. In the pursuit, Idas killed Castor. Pollux, grief-stricken, begged Zeus to allow him to die in place of Castor. Zeus then permitted both Castor and Pollux to live in Hades one day and on Mount Olympus the next. According to one version of the story, Zeus placed the brothers among the stars after their lives on earth and they became the constellation Gemini, or the twins. The two brightest stars in the constellation bear the names Castor and Pollux.