Mewtwo

Mewtwo is a psychic genetic Pokemon cloned from Mew, the Legendary Pokemon ancestor of all Pokemons. Mewtwo used to be a villain until it became good

Kanto
Approximately twenty years before the present, Team Rocket discovered that a Mew was living in Guyana. Many years later, under the orders of the new boss, Giovanni, an expedition of Team Rocket scientists traveled to the area to search for Fossils. They succeeded in finding an eyelash belonging to Mew. Giovanni asked Dr. Fuji to clone Mew for him and create the most powerful Pokémon in existence. Fuji agreed because he wanted to use Team Rocket's research to attempt to clone his deceased daughter, Amber. One month after the discovery of the eyelash, Mewtwo was successfully created and stored at New Island. At this point, it was still not fully grown and lived in a large test tube beside others containing Bulbasaurtwo, Squirtletwo, Charmandertwo, and Ambertwo. Fuji and Giovanni thought Mewtwo was unconscious inside its tube, but it was able to communicate telepathically with Ambertwo and the other clones. However, because the life force of a human is not as strong as a Pokémon's, the Amber clone died. The other three clones had died shortly before Amber did, suggesting that Mewtwo's life force is even stronger than a normal Pokémon's. Over the years, Mewtwo matured and grew confused over its origin and place in the world. After resolving to figure out where it belongs, Mewtwo broke out of its test tube. The Team Rocket scientists were happy that they had succeeded in creating the most powerful Pokémon in the world, but that joy turned to horror once Mewtwo realized that it was just an experiment and unleashed its fury upon them. Despite the efforts of the security systems that attempted to control it, Mewtwo destroyed the laboratory on New Island and all of the scientists in it.

In his robotic suit, under observance by Giovanni Immediately thereafter, Giovanni found Mewtwo and convinced it to help with Team Rocket's goal of controlling the world. Mewtwo's power was focused as well as restrained by a robotic suit of armor as it performed tasks such as battling for Giovanni in the Viridian Gym and helping Team Rocket capture Pokémon. Mewtwo eventually became tired of being used by Giovanni. It developed a strong hatred for humans and thought that they were weak and selfish beings only interested in power and wealth; it also despised Pokémon who served humans. Mewtwo escaped from Giovanni (destroying Team Rocket headquarters in the process), relocated to its birthplace on New Island and built a castle there. Mewtwo then issued a challenge to several strong Pokémon Trainers, including Ash Ketchum. It used its powers to create a storm that would serve as a test to see who could make it to the island. Only a handful of Trainers managed to brave the storm and arrive, including Ash and his friends. Upon revealing itself, Mewtwo challenged the Trainers with its clone Pokémon—Venusaur, Blastoise, and Charizard—to prove its superiority to human Trainers and the superiority of cloned Pokémon to trained Pokémon. To do this, Mewtwo used a variation of the Poké Balls used by Trainers. Once caught in the Balls, the Pokémon that had been brought to the island were cloned in an upstairs laboratory. However, before Mewtwo could defeat the Trainers and move out into the world, Mew appeared. Mew and Mewtwo fought at length, ceasing only when Ash was caught in their crossfire and turned to stone. After Ash was revived by the tears of the nearby Pokémon, clone and original alike, Mewtwo experienced a change of heart and no longer sought to conquer the world. Mewtwo reasoned that it would be best if no one remembered the events that had transpired, so it erased the memories of all the people and Pokémon and transported them back to the mainland. Mewtwo and Mew left New Island with the cloned Pokémon to seek a proper place for themselves.

Johto
Mewtwo and the clones migrated to Johto and eventually settled on Mount Quena. To prevent any encounters with humans, Mewtwo frequently used severe storms to make the mountain inaccessible. One day, a bus full of people was nearly knocked off the road, so Mewtwo decided to use its telekinesis to place the bus back on the road. It explained to its fellow clones that a bus crash would attract even more humans. However, the clone Meowth believed that Mewtwo's act may have also been due to a growing soft spot for humanity.

Wearing his cape during the introductory sequence of Jirachi: Wish Maker After a few years, Giovanni found Mewtwo's hiding place via one of Team Rocket's satellites and began a plan to capture it once again. However, this plan was foiled when Mewtwo again met with Ash, who did not remember their previous encounter. Giovanni restrained Mewtwo, but his friends helped it to escape and defeat Giovanni. At the end of the ordeal, Mewtwo erased Giovanni and his soldiers' memories and decided to move throughout the world, searching for the meaning of its life. In the epilogue to Mewtwo Returns and in some TV series opening sequences and movie previews, Mewtwo has been seen wearing a plain brown cape and moving across rooftops at night. Mewtwo also had a passing mention in the special The Mastermind of Mirage Pokémon, when the mirage Mewtwo was created, Mirage Master claimed "This is not the Mewtwo you are familiar with", possibly meaning that he saw Pikachu's memory of Mewtwo.

Unova
Mewtwo is set to make another appearance in M16, fighting against the Genesect Army alongside Ash and his friends.

Games
In the main Pokemon games, Mewtwo is only encountered in Cerulean Cave, with no real storyline significance. He is seen at level 70 in Red, Blue, Yellow, FireRed, LeafGreen, HeartGold and SoulSilver.