How they found this mythology..

It originated from Mother Leda, she had twins but different fathers, which is Tyndarus (Castor’s father) and Zeus (Pollux’s father). Castor was a horseman, and Pollux was known for his great strength, both were adventurous known for their good looks. The mortal one, Castor, soon passed away after spending a night together with Pollux. He couldn't move on without having Castor by his side, therefore he decided to ask Zeus for help. Instead of killing Pollux so he can be with Castor in the afterlife, he made Castor also immortal, so that him and Pollux can be together, and is now a Gemini.