Prior to his encounter with the Forever People, Sonny Sumo was an honorable figure who used his prowess in sumo to compete as an underground fighter. Unbeknownst to Sonny or his manager, Harry Sharp, Sonny contained a portion of the Anti-Life Equation that enhanced his ability to harness his chi. The Forever People were able to unlock the Equations powers with their Mother Box, allowing him to recover permanently from wounds sustained in an organized battle against a robot called Sagutai.
Sonny then joined the team in their battle against Desaad, using his unique abilities to force Darkseid's minions in a deep sleep. This event earned Sonny and his allies the ire of Darkseid himself, who used his Omega Sanction to trap Sonny in feudal. He had a happy, remainder of his life there. Or, that was thought to be the case.
In the second issue of Final Crisis, Sonny Sumo is seen living in present day . His role as a fighter has earnt him some level of celebrity with the pop-culture driven youths that frequent metahuman nightclubs, including Super Young Team. Shilo Norman discovers Sonny in the club after a battle with an armored youth called Megayakuza, using his Mother Box to heal his wounds. Sonny joins Shilo in his quest to battle the New Gods who have fallen to Earth. They are soon joined by Super Young Team, before joining the remnants of Checkmate.