The ancient Greeks believed that the constellation Gemini represented the twin horsemen Castor and Pollux. According to one version of the story, Castor was an ordinary human, while Pollux, the son of Zeus, lived forever. Castor was mortally wounded during a battle, whereupon Zeus offered Pollux a choice: he could let Castor die or he could give his brother half his immortality. Pollux chose to save his brother, and forever afterwards they would spend a day Olympus followed by a day in Hades.
“My twin brother died from suicide in 2011,” writes Zach Poynter. He chose to memorialize his brother with two tattoos on his arm. One is of the constellation Gemini. The other is of DNA. “We were identical twins, thus sharing the same DNA (although not expressing it the same way!)” Poynter writes.