The young boy, Alex, was born with a partially developed right arm. The Microsoft OneNote Collective Project, with Albert Manero at the head, has been working to develop an arm for Alex. Given Alex's love of superheroes, they thought it might be fun to bring a larger-than-life bionics expert to help out.
Check out the video in the tweet below.
Downey will appear as Iron Man in Avengers: Age of Ultron, opening May 1.