Now, though, it looks like he might have to fight off some competition - from none other than Mr Robert Downey Jr.
Iron Man himself has been snapped wearing what appears to be a Celtic top in a post which has been shared via Twitter hundreds of times in under 24 hours.
Posted by user @Fitzy_07, he said: “Iron Man Loves The Celtic.”
Supporters couldn’t believe their eyes, with one summing up how many felt.
He said: “Just when I thought @RobertDowneyJr couldn’t get any cooler.”
The post has, however, divided opinion among many, with some questioning whether the image has been doctored or not.
Chat on some forums has suggested the strip was gifted to the 52-year-old New Yorker from a terminally ill Hoops fan, according to one Twitter user.
The snap has come just days after the actor made a young Scots boy’s dreams come true in spectacular fashion.
Iron Man-daft Aaron hunter, from from Alexandria in West Dunbartonshire, couldn’t believe his luck after Downey Jr. gave him a FaceTime call last week following a viral appeal.
In March, the Evening Times reported how the seven-year-old called on the Avengers superhero for help in beating a deadly disease.
In a very touching video, Aaron said: “Iron Man, if you see this I really, really need your help.”