Velvet was a legendary Human magician, and the creator and former owner of Velvet's Hidden Treasury. He stored many rare, unique, and some ancient items in the treasury, items he had collected over his lifetime. He made the Carbuncle, Returner, which managed the Dungeon after he died. He died within his treasury, and remained there, becoming mummified.
Rou much later in the story regrets not eating Velvet or at least his other arm to see if he could get any abilities from a famous ancient magician.