Iron Man was a fictional superhero.
When the Eleventh Doctor asked the 10-year old Joe Hudson if wants to save New York City, Joe Hudson wanted to know if the Doctor was like Iron Man. At first the Doctor said that he was exactly like Iron Man. Then the Doctor mentioned that he didn't have the iron and that he had two hearts. So he was not like Iron Man, but the Doctor added that this wouldn't matter, as he was better than Iron Man. (PROSE: The Forgotten Army)