William Harding was raised in the small city of Royal Peak in the late 19th century. Due to his family's severe poverty, William grew up to be criminal, making his living by staging elaborate robberies and heists. He became a respected member of the Royal Peak criminal underground, eventually plotting the robbery of a middle-ages artifact that is visiting the local museum.
During the heist, one of Harding's men panicked and shot him, leaving him for dead. He was discovered by Dr. Darke, who was investigating the artifact. Darke offered to give him immortality in exchange for his commitment to doing good. Harding agreed, and Darke endowed him with immortality. Darke, seeing the potential in him, also gave him incredible abilities in hopes he could become a force for good.
Harding became a superhumanly strong, virtually indestructible tank of a being. He entered World War I and fought alongside the American forces, doing his best to repay the debt he owed. He vowed to return one day to Royal Peak and take revenge on the men who had corrupted his life.
When the War to End All Wars proved to be misnamed and hostilities broke out again in the very same spot, Harding was redeployed to Europe in 1939. This time he went with in with a group of like-minded associates, which included Captain Redeagle. They formed the world's first team of superheroes. Since his passion for vengeance had cooled over the years, he opted not to use the Avenging Angel codename he had planned on. When he was named leader of the new team project, he opted instead for the more neutral Supreme Commander. They chose the name Knights for the team, because honorable Knights of the Crusades were a favorite childhood subject of interest for him and his old friend Dr. Darke was an expert on the Middle Ages.
The Knights had four years of glorious adventures fighting the villainous Nazis and their minions. During this period the core members formed a strong bond.
Following VE day, as the focus of the War shifted to the Pacific Front, the team's attention was divided among the continents. Supreme Commander and several other members remained behind in Europe to aid in the reconstruction. The rest of the team moved to the Pacific and defended troops there as they prepared for the coming invasion of Japan. This proved a fatal flaw as the menace of the Crimson Dragon arose in Asia. On August 9, 1945, three members of the Knights were killed flying over Nagasaki, Japan, in an atomic bomb blast detonated by the Crimson Dragon. Included in those casualties was his best friend, Captain Redeagle. Harding never forgave himself for losing a second set of brothers-in-arms in a Second World War.
Feeling deeply guilty, Supreme Commander took a hiatus which extended into a full year in order for himself and the team to grieve, consider the possibilities, and regroup. During this time Tom Rush served as interim Team Leader and moved the team to Queen City, USA, and established a permanent headquarters.
When he returned to his leadership role, he embraced his life and heroic function. He recruited new members over the years, including the young Sun Girl, who would later become Solar Queen and his wife.
Following the tragic events of Darke Day, when the destruction of their headquarters and invasion of Earth by the demonic hordes of Dhrell revealed exactly what Dr. Darke had inadvertently done, Supreme Commander felt he had no choice but to defend the Earth at all costs. Repelling the demon king, he then led the invasion of Hell. Things did not proceed as well as planned, so in the end Supreme Commander had no choice but to divide his forces and send half his team back through the portal to defend the Earth while he and the rest remained to fight. He demanded his wife Solar Queen be one of the ones to return to Earth. He was last seen locked in mortal combat with Dhrell and the hordes of Hell when the portal was resealed by Dr. Darke.
Supreme Commander is superstrong. He has lifted many tons, most famously the back end of a sinking battleship. Due to his strength he can leap immense distances. He has great endurance and his skill is virtually invulnerable to injury. He has withstood machine guns blasts at point blank range. With his strength and invunerability, he can punch through rock or steel without injury.