Houseki no Kuni character.
The mysterious instructor, guardian, and father figure to the Gems. His appearance is that of a bald and rather tall Buddhist monk, complete with robes.
The name 金剛 (Kongou) means "Adamant", that is, a mythical indestructible metal or material. In a Buddhist context, it has the additional meaning of a vajra, and symbolically, "the indestructible truth".