LOS ANGELES (Reuters) - Natalie Portman has been cast as the female lead in Thor, Marvel Studios adaptation of its comic book featuring the Norse god of thunder. Kenneth Branagh is directing. Portman will play Jane Foster, who in early comic-book lore was a nurse who became Thors first love. The studio said the character would be updated for the feature adaptation, with Foster a doctor-scientist type. Chris Hemsworth (Star Trek) is already cast as Thor. Tom Hiddleston is Loki, the god of mischief who serves as the movies villain. Thor is Marvels stab at an epic fantasy adventure, spanning from present-day Earth to the realm of Asgard. The story centers on Thor, a powerful but arrogant warrior whose reckless actions reignite an ancient war. As punishment, Thor is cast down to Earth and forced to live among humans. But once here, he learns what it takes to be a true hero when the most dangerous villain of his world sends the darkest forces of Asgard to invade Earth. (Jane) is the human lead, so to speak, who helps ground the film in reality, said Marvels Kevin Feige, who is producing the movie. He added: We wanted to avoid that syndrome of just because the hair is up and theyre wearing glasses it means theyre smart. ... We wanted somebody that can have the chemistry that the best of our Marvel couples have had, whether its Tobey (Maguire) and Kirsten (Dunst) or Tony (Stark, played by Robert Downey Jr.) and Pepper (Potts, played by Gwyneth Paltrow). The film will be released in the U.S. on May 20, 2011, distributed by Paramount Pictures. Portman is about to start work on the comedy Your Highness, directed by David Gordon Green, and in the fall will shoot David Aronofskys supernatural thriller Black Swan. Her comic-book and fantasy movie resume includes the recent Star Wars trilogy and V for Vendetta.