Kryptonite is a fictional element in DC Comics and one of the few items that can harm Superman his cousin, Supergirl and his dog, Krypto.
It is able to kill the Man of Steel should he stay in contact for a long period of time. Some of its notable users are Lex Luthor and Metalllo.
Kryptonite comes in many different forms, though the most infamous is Green Kryptonite - each Kryptonite variant has vastly different properties but are in general harmful to Kryptonians.
However Kryptonite is unique to each universe, meaning Kryptonite from Earth-1 will not work on Earth-3 Superman or vice-versa.. this came into especially great effect with Superboy-Prime, whose universe lacked Kryptonite and thus made him one of the few Kryptonians in existence with a complete immunity to Kryptonite.
the most common and iconic state of Kryptonite which causes great discomfort and weakness in Kryptonians as well as radiation poisoning in other life-forms (for example Lex Luthor contracted cancer from prolonged exposure to Green Kryptonite).
Gold Kryptonite has the ability to instantly depower Kryptonians, unlike Green Kryptonite, prolonged exposure to Gold Kryptonite will permanently depower Kryptonians and deny them the ability to gain superhuman powers, in effect turning them into ordinary humans.
causes Kryptonians to split into two different entities, one embodying the "evil" side of the personality.
- Metallo's Heart is usually made from Green Kyptonite
- Reactron has had a Kryptonite Heart, similar to Metallo, for some time, however his is usually of the more dangerous Gold Kryptonite.
- Green Kryptonite has been fashioned into Kryptonite Bullets and Kryptonite Knives.
- The Laughing Dragon was a statue made out of Green Kryptonite.
- Injustice Batman utilized a Gold Kryptonite Dagger to try and stop Injustice Superman.
- Firestorm is shown to be capable of creating Kryptonite via molecular manipulation.
- in most Superman or Supergirl boss encounters in DC Online the player-villain will use Green Kryptonite to weaken the heroes and allow them to be fought.
- almost all Superman villains have this as their motive due to it being one of the few things capable of harming Superman (Lex Luthor, Kryptonite Man, Kryptonite Woman etc)