I like Superman Junior, from ACTION COMICS #232 (September 1957).
This character, whose name was Johnny Kirk, was sent away on a rocketship by his scientist father after he had noticed that a gigantic asteroid was on a collision course for Earth. He didn't notice until the rocketship took off that Superboy was there to stop it (and indeed he was completely unaware of the existence of Superboy due to his remote location), so little Johnny was lost, seemingly forever, especially after Superboy's search through space came up with nothing.
Anyway, Johnny Kirk grew up on an oxygen-bearing planetoid with no trouble at all due to some strange gas granting him super-powers exactly like those of Superboy. When he was around 12 to 14 he somehow came crashing to Earth, to be found by Superman (this happened a year or so before Supergirl's first appearance, which was quite similar). Anyway, Superman now finally learned what happened to little Johnny Kirk, but since Johnny's long-dead scientist-father had made Superboy swear to be Johnny's parent should he ever be found, Superman decided to "adopt" Johnny as his own. Since he was super-powered, he was given a Superman insignia to wear over the uniform he already wore (don't ask me where that came from -- I have no idea), and the team of Superman and Superman Junior was born.
Meanwhile, Superman assumed the name of Johnny's father, Morton Kirk, and settled in Smallville with Johnny posing as his son. It seemed as if things would continue on as they were, except for the fact that Superman was slowly losing his super-powers, one by one -- it seems as though Johnny had brought back a kind of "super-poison" in his ship, unbeknownst to either of them at the time, and this "super-poison" was acting like slow-acting Gold Kryptonite (which had not yet been introduced at the time) in that it was slowly removing Superman's powers. He kept this a secret, however, and resolved on really being Johnny's father, even as Superman Junior fully took over the duties of Superman due to the latter's eventual forced retirement.
Ultimately, Johnny discovered the truth about what was happening to Superman when Superman talked in his sleep (before you ask, yes -- they actually slept in the same room together, too, so for all we know Superman might make a good member of NAMBLA). Johnny immediately dashed out and found a rare magnetically-charged metal meteor and sent it crashing to Earth. Calling Superman over, he tricked him into touching one side of the meteor as he touched the other. Voila! The electromagnetic charge of the meteor transferred all of Johnny's super-powers to the now-powerless Superman just in time.
So now that Johnny Kirk had made this huge sacrifice, giving the super-powers he had had for almost all of his life to Superman for nothing in return, what does Superman do? He leaves little Johnny Kirk standing on a Smallville street corner as he returns to his old life of Clark Kent/Superman in Metropolis.
Johnny Kirk is never seen again. His ultimate fate remains unknown, yet we can safely assume he grew up emotionally scarred, first by his lonely upbringing separated from humanity and then his second abandonment by a Superman who had broken his promise to take care of him.
Lousy deadbeat dad.
