Just have a look!
Oh well, about Mewtwo... It is very easy and hard to say it. At first, he thinks that he's not complete, because he's a part of the Ancient Pokémon Mew. He can see Mew's pictures of its past, as seen in the movie.
Mewtwo keeping asking who is he, and he can't find and answer this question in his heart and mind, and so it will attack primarily responsible for its non-reason: humans. He wants to prove to himself his power and defeat Mew and wants to prove that he is unique. At the end, we can see that he forgive himself and all his anger, and help and protect all Pokémon with his own power.
Mewtwo is a very brave Pokémon for me, he had an hard life to understand life as an human, now, he thinks as a Pokémon being! :D