See the changing looks of the 'Avengers: Age of Ultron' cast

Avengers fans, it's finally time to assemble.

This weekend marks the opening of Avengers: Age of Ultron, the highly anticipated sequel to the third most popular movie of all time.

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The latest film in the Avengers franchise is named for a villain created by accident in the lab of Tony Stark, aka Iron Man. It's up to the superhero team including Thor, Captain America and the Black Widow to put a stop to Ultron's terrible plans and save the world.

So how has the cast changed since they started their acting careers? See retro photos of Robert Downey Jr., Scarlett Johansson and more in the gallery above.

Avengers: Age of Ultron opens in theaters everywhere on Friday with limited showings on Thursday evening.

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