Castor

In Greek and Roman mythology, Castor and Pollux or Polydeuces were twin brothers, together known as the Discord. Their mother was Leda, but Castor was the mortal son of Tyndareus, the king of Sparta, and Pollux the divine son of Zeus, who seduced or raped Leda in the guise of a swan (Greek myths concerning divine sex are often vague on the issue of female consent). Though accounts of their birth are varied, they are sometimes said to have been born from an egg, along with their twin sisters Helen of Troy and Clytemnestra.

In Latin the twins are also known as the Gemini or Castores. When Castor was killed, Pollux asked Zeus to let him share his own immortality with his twin to keep them together, and they were transformed into the constellation Gemini. The pair was regarded as the patrons of sailors, to whom they appeared as St. Elmo's fire, and were also associated with horsemanship.