Metallo is a supervillain appearing in American comic books published by DC Comics, commonly as an adversary of Superman. He is usually depicted as a cyborg with a kryptonite power source in his heart, which he uses as a weapon against Superman. In 2009, Metallo was ranked as IGN's 52nd-greatest comic book villain of all time.

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 be transmitted 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.