Mewtwo is a Genetic Test subject that was developed on Cinnibar Island. It is unknown what the purpose of it's creation was, but the group behind it assured that it was for a peaceful Scientific purpose that would be able to help humans become stronger, healthier, and impervious to Disease.
However, the Experiment proved lethal, as the experiment turned out to be a secret Pokemon created from the genes of a powerful phsycic creature, the Mythical Mew. So successful was their project that the Scientists of Cinnibar Island, lead by Dr. Fuji, couldn't predict that Mewtwo saw through their deceptive sayings, and it knew it was only made to serve Humans, who, it realized, could be a very cruel and punishing master.
The experiment, Dubbed "Mewtwo" By the scientists, used his phsycic powers to tear the Laboratory down. Dr. Fuji's last words were: "We wanted to create the most powerful Pokemon ever.... and we succeeded.After he demolished the Science facility on Cinibar Island, Mewtwo was approached by Giovanni, who was the head of the team that created the powerful Pokemon. After making a deal with the man powerful in wealth, Mewtwo spent a year training with his powers, wearing a suit of armor that "Focused his psychic abilities." But afterward, he learned from the wealthy man that he was only being used to serve him, again realizing that Humans are only going to further use him for their purposes. In anger, Mewtwo destroyed the complex, flew away, and removed the Armor that covered his body and "Focused", but Suppressed, his powers. He then promised that he would find his own purpose, whether or not anyone helped him or tried to prevent him from getting to his goals.'