Kryptonite
Kryptonite is a fictional material that appears primarily in Superman stories published by DC Comics. In its best-known form, it is a green, crystalline material originating from Superman's home world of Krypton that emits a unique, poisonous radiation that can weaken and even kill Kryptonians. Kryptonite radiation can emit through any element except lead. Thus, Superman has a special lead suit to protect himself from the radiation. There are other varieties of kryptonite, such as red and gold kryptonite, which have different but still generally negative effects. Due to Superman's popularity, kryptonite has become a byword for an extraordinary exploitable weakness, synonymous with "Achilles' heel". Batman, Lex Luthor, Metallo, and Titano are four notable characters often presented as using kryptonite — the first carrying the substance as a last-ditch method to stop his ally Superman if he is subject to mind control or otherwise compromised, the next two using the mineral to ward off Superman or incorporating it into weapons, and the fourth being able to project rays of kryptonite radiation from his eyes after being altered by simultaneous exposure to kryptonite and uranium. An unpublished 1940 story titled "The K-Metal from Krypton", written by Superman creator Jerry Siegel, featured a prototype of kryptonite. It was a mineral from the planet Krypton that drained Superman of his strength while giving superhuman powers to humans. This story was rejected because in it Superman reveals his identity to Lois Lane. The mineral known as kryptonite, not to be confused with the real element krypton, was first officially introduced in the radio serial The Adventures of Superman, in the story "The Meteor from Krypton", broadcast in June 1943. An apocryphal story claims that kryptonite was introduced to give Superman's voice actor, Bud Collyer, the possibility to take a vacation at a time when the radio serial was performed live. In an episode where Collyer would not be present to perform, Superman would be incapacitated by kryptonite, and a substitute voice actor would make groaning sounds.