The film has been a big hit with critics ahead of its U.S. release on Friday (04May12), and has already topped several other countries' box office charts, including Australia and the U.K.
But Evans, who plays Captain America in the blockbuster, believes the movie wouldn't have worked without the Iron Man star.
Evans tells U.S. show Good Morning America, "I kind of give a lot of credit to Downey. He's kind of the father of this group. He came to the set with such a positive attitude and has such a great demeanour. We all kind of fell in line as a result of his disposition. He's just an amazing guy and he made it a really family atmosphere right away."