Bizarro is a villainous and imperfect clone of Superman.
Lex Luthor came up with the idea of creating his own Superman through cloning. He hired Dr. Teng, an expert in cloning, but because Superman was an alien and the process was designed for cloning humans, the clone morphed into a monsterous brute. Luthor jokingly called it Bizarro and the unintelligent creature quickly went on a rampage through out Metropolis and kidnapped Lois Lane. Superman managed to defeat him relatively quickly as he disintegrated from weak cellular structure. Luthor attempted to make a superman clone again, but once again it morphed into Bizarro. Retaining some of Superman's memories, Bizarro constructed his own "Bizarro Metropolis" out of trash and kidnapped Lois Lane.
It has been suggested that the Bizarro character, who is the opposite of Superman and all he stands for, was a metaphor for the Soviet Union at a time when Superman was seen as the embodiment of the United States in the 1950s. The Soviet reference was likely akin to the fact that the USSR was athetically prominent in events like the Olympics and had a military that made great contributions to winning the Second World War, but in civilian life many aspects of the Soviet economy were dysfunctional.
The original Bizarro was created when Superman was exposed to a "duplicate ray." In accordance with the science fiction concepts of Superman stories of the era, Bizarro relocated to "the Bizarro world," a cubical planet called Htrae which operated under "Bizarro logic" (it was a crime to do anything good or right) and which Bizarro populated with inverted versions of Superman’s supporting cast and other DC heroes.
The 1986 event Crisis on Infinite Earths rewrote DC’s continuity, eliminating Htrae. Since then, two Bizarro characters have appeared, one of them a flawed clone created by Lex Luthor. The second, longer lasting Bizarro, was an idea of the Batman villain the Joker, brought to life by the cosmic trickster Mister Mxyzptlk.
Bizarro has been a consistent enemy of Superman since his first appearance. Faithful adaptations of Bizarro appeared in the animated series Super Friends and series in the subsequent DC Universe. Also, doppelgängers of Superman with some attributes of Bizarro appeared in live action adaptations.
Bizarro and the Bizarro World have become somewhat well known in popular culture, and the term Bizarro is used as to describe anything that utilizes twisted logic or that is the opposite of something else.
DC Animated Universe
Bizarro appeared in Superman the Animated Series as a prototype for an army of Superman clones being manufactured by Lex Luthor. He attempted to be a hero, but was far to destructive to be of any real help. Superman usually showed up to fix Bizarro's "heroic actions". Bizarro then attacked the laboratory in frustration causing it to self destruct. Bizarro, unknown to Superman, survived the explosion and wandered aimlessly ending up at the Fortress of Solitude. While there he destroyed the place and was convinced by the Brainiac orb to be the real Superman. Deciding he needed to rebuild Krypton, he returned to Metropolis and began destroying and rearranging it to look more like "his home planet". Superman intervened once again.Superman, feeling bad for Bizarro's miserable life, took him to a new planet that could sustain life, but nothing lived there except one creature. Bizarro made this creature his pet, dubbing it Krypto, and was happy there until Mister Mxyzptlk arrived. He convinced Bizarro that Superman put him there out of jealousy. Bizarro returned to earth and battled Superman again. Superman convinced Bizarro Mxyzptlk had tricked him, and Bizarro was returned to his homeworld. At some point, for reasons never explained, Bizarro returned to earth and teamed up with Giganta to break Gorilla Grodd out of prison. Wonder Woman and Longshadow stopped them. He would later be a member of Grodd's Legion of Doom.
Bizarro also appeared in the TV series Superboy. This Bizarro was created by a duplicator ray that hit Superboy. Initially an enemy, Bizarro's lonliness made him somewhat of a tragic character. He used the duplicator ray to make his own version of Lana Lang, Superboy's girlfriend. Bizarro Lana teaches him right from wrong. After that Bizarro and Superboy become friends, even calling Superboy his brother.
SmallvilleBizarro also appeared in Smallville. This clone of Superman was actually perfect, and lived with Lana Lang for two weeks without her realizing it wasn't Clark Kent. Though he is never called Bizarro, the episode was named Bizarro and his powers increased in the presense of Kryptonite just like Bizarro. Using Blue Kryptonite, which would render normal kryptonians powerless, Bizarro gained too much power and exploded.