Kryptonite is a mineral from the Superman mythos, originating in the Superman radio show series.

The material is usually shown as having been created from the remains of Superman's native planet of Krypton, and generally has detrimental effects on Superman and other Kryptonians. The name "Kryptonite" covers a variety of forms of the substance, but usually refers to the most common "green" form.

The word Kryptonite is also used in modern speech as a synonym for Achilles' heel, the one weakness of an otherwise invulnerable hero.

Original versions

A forerunner of the kryptonite concept was the unpublished 1940 story "The K-Metal from Krypton", by Superman co-creator Jerry Siegel.Fact: date=February 2008 The K-metal in the story was a piece of Krypton which robbed Superman of his strength while giving humans superpowers, a plot point which made its way into the tv series Smallville.

"Kryptonite" was introduced in 1943 on the Superman radio series, as both a plot device and to allow Superman's actor, Bud Collyer, to occasionally take time off. The substance played a part in at least one major plot-line during the course of the program.

It was not until 1949 that the comic book writers incorporated it into their stories, as both a convenient danger and weakness for Superman and to add an interesting element to his stories. Kryptonite is most commonly depicted as green in coloring, with a few exceptions; it was red in its first appearance in Superman (volume 1) #61 in 1949. When Superman followed the time trail of a piece of red rock that weakened him, he was able to trace his origin back to Krypton for the first time. Other colors of kryptonite, having different effects, began to show up frequently beginning in late 1950s comics, reaching a peak in appearances in 1960s Superman series.

Kryptonite was depicted as being so abundant that many ordinary criminals kept a supply as a precaution against Superman's interference. They kept it hidden so Superman would not be able to steal it and destroy it. In an effort to reduce the use of kryptonite in Superman storylines, all known kryptonite on Earth was transmuted into k-iron in a 1971 storyline, though kryptonite could still be synthetically manufactured by a variety of known and unknown means, and additional material left over from the destruction of Krypton would continue to fall from space.

Post-Crisis Versions

While quantities of Kryptonite are reduced, the material is still present Post-Crisis, albeit only in its green form. However, through the use of Batman's notes, Ra's al Ghul is able to fashion a synthetic Red Kryptonite. Even after quantities have been reduced there's still a fair amount of Kryptonite available, which prompts Superman-friendly corporations, such as Wayne Enterprises and Kord Industries, to take it upon themselves to round up all remaining pieces so as to make its acquisition by small-time crooks more difficult.