Superman III (1971)

Superman III, before earning his S emblem by Curt Swan and Joe Staton, Superman #354, 1980

Clark Kent recalls his alternate self, by Swanderson

The final duplicate of Superman I and Superman II, composed of an "artificial, unstable protoplasm."

Superman III dies saving his alternate version of Earth, one of many Parallel-Worlds, "from a catastrophic explosion caused by a new from of energy!"

Superman learns of these events when he is accidentally transported by historians to the Twenty-Fourth Century of this parallel Earth along with parallel versions of George Washington, Abraham Lincoln, and George Custer (Act No. 399/1, Apr 1971: "Superman, You're Dead ...Dead ...Dead!").