Sumo was a Gotham City gangster who worked for Mr. Squid. He was noted for his large size and the tremendous strength that came with it. Aside from this, however, there was nothing especial about Sumo.
Due to his large size and insane attitudes, Sumo was locked up in Arkham Asylum where he confronted the Resurrection Man. His first attempt at escape was thwarted by the Batman, although he later did escape and came into acquaintance with Mr. Squid. Under Squid, Sumo began to illegally transport child slaves through shipping containers. His association with Squid led to him being attacked by the Batman and brutally beaten.