In which film is Loki 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? Who played Loki in 'Thor'? Who played Natasha Romanoff in 'The Avengers'? Who played Bruce Banner in 'The Avengers'? Who played Clint Barton in 'The Avengers'? In which film is Clint Barton a character?