Castor and Pollux (or Polydeuces) are twin half-brothers in Greek and Roman mythology, known together as the Dioscuri or Dioskouroi.

In Latin, the twins are also known as the Gemini (“twins”) or Castores, as well as the Tyndaridae or Tyndarids. 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 were regarded as the patrons of sailors, to whom they appeared as St. Elmo’s fire.