Who played Loki in 'Thor'?

In which film is Bruce Wayne a character? In which film is Tony Stark a character? Who played Steve Rogers in 'Captain America: The First Avenger'? In which film is Steve Rogers a character? In which film is Loki a character? Who played Natasha Romanoff in 'The Avengers'? Who played Bruce Banner in 'The Avengers'? Who played Clint Barton in 'The Avengers'?