Kryptonite is the element which is Superman's greatest weakness.
A Kryptonite meteor crashed into a river in Africa where its substance became filtered and a mynah bird drinking from the water. As a result, the bird began to develop increased intelligence at a fast rate with this culminating in the ability to speak. Professor Lang found the bird and took it back with him to Smallville where he revealed it to the crowd. The bird began to develop abilities on part with Superboy and escaped from his cage where he began to team up with a local criminal who named him Socrates. Superboy looked to stopping the bird by exposing him to the Kryptonite meteor thus depriving Socrates of his intelligence and returning him back to his original state. (Adventure Comics v1 #225)
After facing numerous defeats by Superman, Intercrime looked to find a means of eliminating the Man of Steel. Thus, they secretly began Project Green under the direction of Dr. Kane. This experiment sought to create a new Kryptonite Man by replacing the blood of a volunteer with liquid green Kryptonite. The volunteer severed an adverse reaction and died but Dr. Kane decided to use the procedure on himself after making some minor corrections. This led to his transformation into Dr. Kryptonite who was a living weapon against Superman. (Action Comics v1 #349)
Batman maintained secret detailed files on his fellow Justice League members including schemes on how to defeat each of them. Among these included experiments on Kryptonite that altered its radioactive half-life to make it less lethal but the pain more agonising against Kryptonians. Thus, this sample of Red Kryptonite was kept in secret and intended for use against Superman. Ra's al Ghul managed to uncover these plans and acquired a sample of it which was given to Talia al Ghul for use against the Man of Steel. (JLA v1 #44)
A large asteroid made of Kryptonite that was a mass from the remains of Krypton went into space and headed towards Earth. It was detected on Earth where it was designated as Asteroid 921 Wormwood with President Luthor looking to stop it from impacting the planet. (Superman/Batman v1 #1) A giant space capable mecha was created by the Toyman Hiro Okamura with this being commandeered by Captain Atom who piloted it to stop the meteor. With the giant craft, he managed to shatter the asteroid before it could crash onto Earth causing various types of Kryponite to fall onto the surface with the hero community looking to gather and contain their spread. (Superman/Batman v1 #6)
At some point, the presence of the once rare Kryptonite had become more widespread to the point where it became used for everyday items such as engagement rings or parts of props with the substance selling in Gotham City for $1000 a gram. Superman thus decided to enlist the aid of Batman in gathering all the Kryponite on the planet in order to dispose of it so that it would not be used as a weapon against him. (Superman/Batman v1 #44) This led to the pair with other heroes that volunteered to start gathering the Kryptonite that was to be buried in a secure mountain facility. To accomplish this, a special suit was made for Superman so that he could handle Kryptonite without suffering the adverse effects from exposure to its radiation. (Superman/Batman v1 #45) After removing Metallo's Kryptonite heart, they next found a signature for a new form of Kryptonite and traced it to the Oblivion Bar. Once there, they found it an ancient mystical artefact called the Ach-om Rashay that was also known as the Amulet of Mindfulness. This relic contained a core of Silver Kryptonite that attracted the attention of Superman who was exposed to its power. It rendered him unconscious briefly and gave him effects similar to drug use such as loss of inhibitions, altered perceptions, extreme hunger cravings and other hallucinogenic effects. The Justice League later discovered that a cure to its power was the twin amulet that was located on Dinosaur Island where they returned Superman back to normal. (Superman/Batman v1 #46) At some point, the U.S. government began to secretly gather Kryptonite that they stored at a secure facility in Kansas as they weaponised it for possible use against Superman as part of a project headed by Amanda Waller. Several military officers who volunteered were later exposed to it giving them Kryptonite based powers with these being part of a elite team called the Last Line. Superman and Batman tracked the Kryptonite to the facility leading to a conflict with the Last Line. (Superman/Batman v1 #47) After defeating them, Superman learnt that the supplier of the Kryponite based weapons was LexCorp with Lana Lang having agreed to the U.S. government contract in order to produce revenue for the financially struggling company. The Man of Steel attempted to forcibly remove LexCorp's supply of Kryptonite though Lang revealed that there were dozens of hidden caches which she was prepared to detonate to litter the atmosphere with micro-K which would be toxic to Kryptonites if Superman forced the issue. Superman decided to take the Kryptonite leading to Lang detonating the caches making the planet toxic to Kryptonians though Hiro Okamura used nanite machines to clean the atmosphere of the micro-K. Afterwards, Superman took the collected Kryptonite him and Batman had gathered which he threw into the sun to dispose of it. (Superman/Batman v1 #49)
K. Russell Abernathy who headed a scientific start-up R&D lab in Metropolis experimented with Kryptonite as he sought to develop it into a new energy source. The experiments involved animal testing with an accident occurring in the lab which bathed him in the radiation turning him into the Kryptonite Man. He went on a rampage until Supergirl arrived on the scene and managed to apprehend him. (Superman v1 #650)
Element created from the substance of the planet Krypton after its destruction. A radioactive element, it has a half-life varying between several years to a century long. There are a number of varieties and isotopes of kryptonite, which (unless otherwise noted) only affect Kryptonian lifeforms. All Kryptonite eventually decays to iron. Unlike most Kryptonian materials, Kryptonite does not become invulnerable under a yellow sun- but it does become friction-proof, thus able to withstand atmospheric entry.
This variety weakens and eventually kills only super-powered Kryptonians (as in, dwelling under a yellow sun). This is the most common form.
This variety weakens and eventually kills non-super-powered Kryptonians (dwelling under a red sun). Argo City was built on Anti-Kryptonite, which was responsible for destroying most of its population.
An isotope of Green Kryptonite accidentally created by Supergirl when she was trying to find a cure for Kryptonite poisoning. X-Kryptonite gives temporary Kryptonian super-powers to Earth life forms.
Created in an unrepeatable experiment on Earth, it affected humans the same way Green K affects super-powered Kryptonians.
Normal Green Kryptonite which was altered by a weird space cloud. A piece of Red Kryptonite has the same, unpredictable effect on every Kryptonian who encounters it, generally in the form of physical mutations and/or mental transformations. Its effects last between 24 and 48 hours, and after a Kryptonian is affected by an individual piece, they are thereafter immune to that piece. However, since Red K is so bizarre and random in nature, there are certainly exceptions.
This variety emits radiation that can kill plant life of any world, not merely that of Krypton.
Created from Green K by the same process that created Bizarro, and only affects Bizarro-Supermen, working in the same way on them as Green K does on Kryptonians. (Note that they were grateful to Superman for creating something that can destroy them.)
A variety permanently robs a Kryptonian of their super-powers. It is believed to be created by subjecting the Red or Green varieties to intense nuclear radiation.
A variety deliberately created by the time-travelling Phantom Zone Criminal Jax-Ur, who prepared crystals from the Jewel Mountains of Krypton to change into Jewel K upon Krypton's end. It was used by the Phantom Zone Criminals to give them psychic abilities projecting outside the Zone, but Superman since destroyed most, if not all, of it.
A likely variant on Red Kryptonite, this type made Superman act effeminate.
Pre-Crisis, Earth-2 and Earth-3
These myriad varieties of Kryptonite ceased to exist after the Crisis on Infinite Earths, though the element can still be found in certain hypertimelines. In fact, samples of Green, Blue, Gold, and Red K can be found in the Planet Krypton restaurant in Metropolis. These varieties also survived in the Pocket Universe.
Post-Crisis, Post-Zero Hour
Element created from the substance of Krypton after its destruction. This element is radioactive, and can weaken and kill a Kryptonian in a relatively short amount of time. However, the radiation also affects non-Kryptonian life as well, slowly causing the effects of radiation poisoning, as Lex Luthor was unfortunate enough to find out.
A Red Kryptonite variety was created by Mister Mxyzptlk, but it was only really a device by which to grant Lex Luthor a wish. Another form of Red Kryptonite- an altered version of normal Kryptonite conceived by Batman as a possible last-ditch weapon against a dangerous Superman- could cause Kryptonians intense, incapacitating agony.
It was known to possess its own beta decay signature. (Superman/Batman v1 #44)
It had horrible effects on living beings with it mutating life into more monstrous forms. (Superman/Batman v1 #45)
Special rays were capable of breaking down solid Kryponite and turning it into Liquid K that could be used to make a serum. However, subjects could experience severe physiological reaction to the liquid Kryptonite and die as a result. (Action Comics v1 #349)
- Dr. Kryptonite : Dr. Kane was a male Intercrime scientist who was involved in Project Green to create a Kryptonite Man to eliminate the Man of Steel but after the volunteer died he decided to subject himself to the procedure himself thus becoming Dr. Kryponite who became a living anti-Superman weapon. After testing his powers on Krypto, he disguised himself as a wrestler called the Mummy who was wrapped up in bandages where he challenged Superman who was unaware of his foes Kryptonite based nature. Kane overwhelmed Superman through Kryptonite radiation but was defeated when aliens from the vegetation world of Flordis abducted him thinking he was their missing king. (Action Comics v1 #349)
- All-American Boy : (Superman/Batman v1 #48)
- The pre-Crisis pink kryptonite was a post-Crisis invention of Peter David in the last issues of Supergirl.
In other media
- In Batman vs. Superman: Dawn of Justice, Kryptonite featured in the setting of the live-action film. It was stated to be a xenomaterial present onboard Kryptonian ship that had a degenerative effect on Kryptonian cells. Large chunks of Kryponite were present at the site of the destroyed World Engine. Lex Luthor initially desired the xenomaterial to be transported to him but was denied the license by Senator Finch leading to him smuggling it onto a ship named the White Portuguese.