In 1997, Superman Red and Superman Blue began as the next in a long line of 1990s-era publicity stunts, including The Death of Superman, and The Death of Clark Kent. The resulting storyline flopped with readers and critics.
Superman began to develop energy-based abilities after troubles he believed stemmed from a natural evolution of his "classic" powers. His condition was unstable and eventually forced him to adopt a blue and white containment suit. He also gained the ability to turn his powers "off," though this left him as vulnerable as a normal human.
Eventually, Superman split into two beings who represented different aspects of his personality, though each believed himself to be the original. After an encounter with the planet-threatening Millennium Giants, the Supermen merged and Superman returned to his normal powers and classic costume. The explanation is vague; Superman felt he was "rewarded" for saving the world, although he claimed in a JLA storyline that he returned to normal when his electromagnetic energy dispersed.
The original Superman-Red/Superman-Blue tale from the 1960's was an imaginary story from Superman #162. In the story, Superman invents a machine powered by various types of kryptonite in an attempt to increase his intelligence. Superman had decided he wanted to finish his list of unaccomplished goals, including the enlargement of the Bottle City of Kandor. The machine worked, increasing Superman's intelligence a hundred fold, but with the unexpected side effect of splitting Superman into two beings, Superman-Red and Superman-Blue.
The twin Supermen successfully enlarged Kandor, freeing its citizens from their bottle prison. They then drew the remnants of Krypton together, creating a "New Krypton." The split also solved the love triangle between Superman, Lois Lane, and Lana Lang. Each woman claims her own Superman, and they have a triple wedding: Superman-Blue marries Lana, Superman-Red marries Lois, and Lucy Lane marries Jimmy Olsen. Superman Red and Superman Blue appear in a panel in 'Infinite Crisis', when Alexander Luthor was trying to fuse the many alternate Supermen.