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
A little sneaky this one but a hint is mentioned four times