Reiner has short blond hair, hazel eyes, and a defined facial structure. His large height, broad shoulders, and serious expression give him an intimidating presence. He's a Marley Warrior, illegitimate son of an Eldian and a Marleyan and grew up in Liberio's internment zone. He infiltrated Paradis Island alongside Berthold, Annie, and Marcel, who died before they could accomplish the mission. Reiner developed serious emotional and mental problems as a result of living a double-life.