Spinel

It was one of the spinel prototypes, created by yellow diamond. it was the closest to the spinel they were looking for, but not enough to become pink diamond's playmate
was kept by yellow diamond as her companion for a while, until he decided to retire from the Gem Homeworld

He has trust issues, if he suspects that you are lying to him, he will begin to behave intensely and aggressively.
His trust issues are the reason his eyes are dilated, but he maintains the cartoonish glow.