Rhinestone was a gem that was genetically engineered by Homeworld scientists in an effort to make the perfect infiltration unit. They succeeded in this, but the design was heavily flawed; Rhinestone was an incredibly pale, sickly, and malformed, however, the scientists in charge of the project wanted more from the raw potential hidden under many flaws. He was given a proper humanoid form after 3 months of testing, yet his color was always fluctuating, until he found a way to control it. After the repairs and perfection process was done, Rhinestone escaped from the clutches of the Homeworld gems, and found himself stranded on Earth, where he was accepted by the Earth Gems.
Rhinestone is often in a happy mood with a cheerful exposition, however, he can be known to be ruthless in combat, showing no quarter to those who hurt his allies.