Pollux, the divine twin son of Zeus and Leda, chose to share his immortality with his brother Castor.
Pollux and Castor were known together as the Dioscuri, or Dioskouroi. In the best-known genealogy, Pollux was fathered by Zeus, while Castor was the mortal son of Tyndareus, king of Sparta and Leda’s husband. Their unusual twin relationship explains why myths portray one brother as immortal and the other as mortal, although ancient sources vary on their parentage and status.
The brothers were renowned horsemen, boxers, hunters, and adventurers. They joined the Argonauts and were associated with the rescue of their sister Helen. After Castor was fatally wounded in a conflict with Idas and Lynceus, Pollux refused to remain immortal without him. He asked Zeus to let them share immortality, and the twins were placed among the stars as Gemini, alternating between Olympus and the Underworld in some accounts.
The common mix-up is reversing their roles: Pollux was the immortal twin, while Castor was the mortal one in the familiar version.