>>43013051It happened in Infinite Crisis.
After the the Crisis on Infinite Earths, Superman of Earth-2, the earth that all Golden Age DC stories took place on, the original Superman from Action Comics #1, went to live in a Paradise Dimension created by Alexander Luthor Jr. of Earth-Three, along with Alex, Lois Lane of Earth-2 (who had since married her Superman), and Superboy of Earth-Prime, making them the only characters to not be changed by the universes merging together.
In Infinite Crisis they break out because Alex has convinced them that the one universe that's left sucks now because it's too grimdark, but Superboy-Prime becomes the very thing he hates when he becomes the grimdarkest character there is. He realizes this but blames everyone else instead of taking responsibility, throwing a massive bitchfit and killing a bunch of people, which makes Superman of Earth-2 switch sides and turn against Superboy-Prime. Long story short, this results in Superman of Earth-2, the original superhero, getting killed by a character that most of /co/ hates.
but I think Superboy-Prime is a pretty cool character and I appreciated the symbolism of him killing the ultimate symbol of wholesome good. Still a sucky way for the original superhero to die, though.