Who played Thanos in 'Avengers: Infinity War'?

Who played Clint Barton in 'The Avengers'? In which film is Clint Barton a character? Who played Nick Fury in 'The Avengers'? In which film is Nick Fury a character? Who played Peter Quill in 'Guardians of the Galaxy'? In which film is Peter Quill a character? Who played T'Challa in 'Black Panther'? In which film is T'Challa a character?