3. Iron Man (2008)
Iron Man was the first movie of the Marvel Cinematic Universe to be released. The film portrays the story of Tony Stark. He is kidnapped by terrorists and attempts to develop a suit that will help him escape.
He later destroys the armored suit in the desert and starts secretly building an improved version of it. This is how he becomes Iron Man.
The film also shows Nick Fury inviting Tony Stark to join The Avengers in a scene after the credits.