Spending some time in Smallville, Superman encountered beings who seemed to posess knowledge of his secret identity.
Even more strange, these youngsters claimed that they were from the 30th century, and that they had been good friends of
his--when he was the hero known as Superboy!
The youths from the future were members of the Legion of Super Heroes. As it happened, during what they thought were trips to Earth's past, they had in fact been diverted into a small Pocket Universe--a sliver of reality containing an entire universe, created and manipulated by the Legion's deadly enemy, the Time Trapper.
Superman and the Legionnaires--Brainiac 5, the Invisible Kid, Sun Boy, and Blok--travelled to this Pocket Universe, where
Superman found a Smallville strangely similar to, and yet oddly different from, his own. Superman met the Legion's
"Superboy"--a younger version of himself, already wearing his famous costume!
Superman left that strange reality and returned to his own with the aid of the Legionnaires, certain that he'd heard the last of this strange Pocket Universe. He was wrong.
Some time after his return, Superman met yet another young hero wearing a costume similar to his own. This time, however,
it was a young girl who bore an uncanny resemblance to Clark Kent's good friend, Lana Lang! This so-called Supergirl claimed
that she had been sent from the Pocket Universe to seek Superman's assistance.
Superman travelled with her back to the Pocket Universe, and found to his horror that the Earth there was completely dead --destroyed, he soon learned, by three Kryptonian villains who had been released from the Phantom Zone, an interdimensional prison created by the Pocket Universe version of Jor-El.
These three--General Zod, Quex-Ul, and Zaora--had no sooner escaped than begun the total subjugation and destruction of the Earth, until barely anyone was left alive. Superman, along with a small band of resistance, faced off against these insane criminals, but the odds were against him. His allies were quickly dispatched, including the Supergirl--a protomatter creation with unique shape-shifting abilities. Superman faced the Kryptonian criminals alone.
In the end, Superman was able to triumph by obtaining something called "gold kryptonite," which Superman discovered robbed
the villains of their superhuman powers. But they claimed that they would not be stopped, that they would get their powers
back and come after Superman and his Earth. Faced with this possibility, Superman felt he had no choice. He exposed the
criminals to the Pocket Universe's version of green kryptonite, killing them.
Superman returned to his own universe, bringing "Supergirl" with him. He tried to return to his life as it had been, but the overwhelming guilt of what he had done bore heavily on his conscience. Friends and colleagues noticed a change in behavior for both Superman and Clark Kent--he became distant, withdrawn, and depressed. His subconscious mind created an alternate personality--Gangbuster, who fought crime with a vicious brutality that made the Batman seem tame by comparison.
An encounter between Superman/Gangbuster and the Guardian of Metropolis served as the wake-up call the Man of Steel needed.
Realizing the danger he had become to those he'd sworn to protect, Superman exiled himself into deep space, intending never
to return to Earth again.
Follow Superman into exile.