Why is James a antagonist in twilight?

He is obsessed with her because of her smell. She smells like that to all vampires.

In the book its also because of the way Edward protected her. When Edward got into a defensive position to defend Bella, James made it like a game. James then tells Bella that he has her mother. Later, Bella finds out that James went through her videos and found one that convinces Bella that her mom is in there.