Note: This version is only based on Mewtwo shown in the Anime series/movies. For more about the main version of him, he can be found here: Mewtwo.
|“||I am the most powerful Pokémon of all; stronger even than Mew.||„|
|~ Mewtwo showing his fury|
|“||Quiet human, from now on, I make the rules.||„|
|~ Mewtwo, while possessing Nurse Joy, to a trainer.|
|“||You humans are a dangerous species...you brought me into you're world with no purpose but to be your slave...but now I have my own purpose...my storm will create my own world...by destroying yours....||„|
|~ Mewtwo (Anime) revealing his plan and his misanthropic personality.|
Mewtwo (Anime) is the main antagonist of Pokemon: The First Movie. His goal was to destroy all humans and their Pokemon, and repopulate the world with clones of Pokemon but later would reform and help the heroes.
According to "The Origin of Mewtwo", a piece of bonus footage included with the Mewtwo Returns DVD which expands his back-story, he interacted with several clones of a Charmander, Squirtle, Bulbasaur, as well as a clone of Amber, the daughter of Dr. Fuji. He was eventually distraught over his friends, especially Amber's premature death, which also resulted in the scientists injecting him with a serum that removed his memory of her, which is strongly implied to have impacted his behavior in the film.
However, Mewtwo was angered by the team as he heard that he was to be controlled by them, and that he may not be part of God's creation, and in his fury, destroyed the lab where he was created, and killed all the scientists with his intense psychic powers. He then allied himself with Giovanni under the promise of learning to control his powers, although he later rebelled from Giovanni after learning that Giovanni's claim of partnership had been a lie, and he had already been sickened by Team Rocket's actions towards Pokémon. Believing humans as oppressors of Pokémon, he vowed to exterminate humans and all Pokémon that sided with them, believing it to be his "purpose". He also wishes to exterminate his predecessor Mew, as he believed he was vastly superior to his genetic counterpart. He eventually saw the errors of his ways shortly after Ash Ketchum sacrificed himself to stop their fighting and all the touched Pokemon use their tears to revive Ash. Departing with Mew and the other Pokémon clones, Mewtwo removed their memories to avoid being tracked down.
Mewtwo serves as an anti-hero in Mewtwo Returns. He was hiding in Kena Mountain with the other clones. He saved a bus with passengers, but he claimed to feel no compassion for the humans. When Giovanni managed to find both Mewtwo and the other clones, he decides to help all of the Pokémon. He was proven to be a great ally for Ash and his friends. Later, when Ash told him he will tell Professor Oak about him and the source, Mewtwo wanted to erase their memories again. But Meowth managed to convinced Mewtwo that they should keep their memories. Mewtwo agreed to let them remember him and the others but he only erased the memory of the people who wanted to destroy them.
Mewtwo's uniqueness largely stems from his psychic abilities. However, his personality is one of the defining points in the Pokémon series. Mewtwo's personality is initially complex involving existentialist anxiety, and contemplating the meaning of existence. His temperament is very withdrawn, introverted, and contemplative, consisting of hate and anger towards humans and his creators.
Having been brought into existence through artificial means, Mewtwo quickly turned on his creators when he learned that they intended to experiment on him further. Feeling betrayed by the very humans that had created him, he decided to forge his own path. The recurring theme in the movies is Mewtwo harboring jealousy towards Mew because he is a copy or derivative, whereas Mew is the original.
In the first movie, the path that Mewtwo has taken makes him into a rather cruel, immoral, nefarious, and calculating character. He frequently exhibits cruelty, and at several intervals, goes so far as to attempt to (or forthrightly) kill those who oppose him. He also shows no qualms about forcing Nurse Joy to serve as his puppet, and then casting her aside once she was of no further use to him. This makes Mewtwo easily one of the most manipulative and malicious characters in the series and the main antagonist in Pokémon The First Movie, prior to his change of heart at the end of the first movie.
However, in Mewtwo Returns, he is much more kind, lenient, and sympathetic, and only wants to protect the other clones that he created. He even protected some humans that were on a bus getting thrown around by strong winds. Therefore, Mewtwo is a hero in his second movie, and a victim. When Giovanni comes on the mountain, Mewtwo is willing to sacrifice himself to save the other clones, as well as Ash's Pikachu and Team Rocket's Meowth. Also, he constantly wants to avoid fighting, which is the exact opposite of the way he was in the first movie.
So, it can be said that Mewtwo (upon Ash's sacrifice in Mewtwo Strikes Back) has become a hero instead of a villain. He continues to live in Johto and, as said by himself, "in shadows".