Jane is one of the Volturi's guard. She is described as small, childlike, and apparently terrifying to other Meyerpires. She is also apparently a sadistic little thing, whose lovely Meyerpire gift is filling people's minds with unbearable agony while smiling sweetly at them. This gift makes her both one of the coolest meyerpires in the books, and about the best candidate for a real villain that there is in this pathetic excuse for a book series. Unfortunately her gift does not work on Bella, proving that fate (or at least Smeyer) has a cruel and twisted sense of humour and that those who most deserve punishment are those least likely to receive it. It is implied that she and her brother Alec were discovered by Aro as humans and changed for their abilities.
Actually it leaves us with the question what characteristic in her real life she had to be as sadistic as she is presented.
will be is portrayed by blond-haired actress Dakota Fanning in the movie adaptation, which she (Jane) may deserve, but Meyer doesn't. Dakota was good at making Jane creepy and cool, and not in such a mustache-twirling way she was in the books.