Superman did die. However, the effect of 30+ years of exposure to the Sun and his placement in the Kryptonian cocoon made it possible for the Eradicator to (inadvertently) resurrect him. It’s like when someone’s heart and brain stop on an operating room table, but the doctor brings them back a moment later – only, because of Superman’s unique physique and the circumstances surrounding his death – it was basically an exhaustion death, not a physical-damage death – he was able to be revived. Even the Eradicator indicated that it was stastically unlikely that such fortuitous circumstances for death would ever occur again.
When Superman died, the Eradicator, who had battled Superman, trying to revert him to a “pure” Kryptonian form on many occassions, went to retrieve Superman’s body. In the process, he absorbed matter from Superman’s tomb, and took a physical form very similar to that of Superman. He incorporation, and confusion, led to a sort of delusion where the Eradicator thought he was Kal-El. He placed Superman’s body in the Kryptonian Matrix to process solar energy and provide the Eradicator with a source of power by which to replenish his own limited abilities.
The Matrix re-stimulated Superman’s organs to the point that they resumed biological function. Like shocking a heart when it stops.
Contrary to what is written by previous posters, the entire Reign of the Supermen story was plotted out months in advance at the Super-Summit of 1991. Originally, Superman was supposed to get married in issue 75, but Lois & Clark screwed that plan up, so they killed him, and let each of the four Superman books create their own new Superman. Like all Superman stories of that period, the entire plot arc was designed by the writers and editor at the Summit, and then everyone when back to their home towns to write from afar. It was known from the beginning which characters would be ‘good,’ which would be ‘bad,’ and which would end up dead.
Cyborg Superman’s origin began in a comical tale that was meant to spoof the Fantastic Four. A space shuttle crashed, resulting in the mutation of its four inhabitants, but with disastrous results. The only survivor, Hank Henshaw, became incapable of living on Earth over the grief resulting from the deaths of his wife and two other co-astronauts. Having been bonded to technology, he stole Superman’s gestation matrix, which had brought Kal-El to Earth, and departed to find a new life in the cosmos as a living machine. Instead, he went crazy, and blamed Superman for the death of his crew. Since the Matrix had a recording of Superman’s early years, and knew Superman’s DNA, and was Kryptonian in origin, he was able to fashion himself a Kryptonian-tech, Superman-DNA’ed body with which to return to Earth.
He was quite mad, so it is possible that at times, he really did think he was Superman.
I consider the mid-1990s to be a real high point for recent Superman comics. The Death/Funeral/Return story, followed by the Clone Plague and the Fall of Metropolis, then by the Wedding, Superman Blue and finally the rise of Lex Luthor to the presidency, was all a lot of fun. What I liked most was that each book led into the next week’s book, like a TV show. And the supporting cast was broad, consistent and had their own plots.
Nowadays, the Superman books are all action, the supporting cast is pretty much non-existent, and all the books follow their own storyline, which makes continuity a pain (when does book X take place in comparison to book Y? I can never tell!). Well, Superman itself isn’t action-oriented. Instead, it’s just issue after dreadful issue of Superman chatting with a priest.
I miss Cadmus, Supergirl/Matrix, Cat Grant, GBS, Keith White, Luthor as corporate leader, and all the rest from the good old days. These comics just ain’t what they used to be.