In a recent interview with Esquire;
Writer Scott Raab interviewed the actor for the new issue of Esquire. “Downey told me: ‘We wanted Bill to consider a role in Iron Man, but nobody could find him,’” Raab told Murray. “Show people are awestruck by your inaccessibility.”
“I’m not trying to be coy,” the actor replied. “It’s just practical for me. When the phone started ringing too many times, I had to take it back to what I can handle. I take my chances on a job or a person as opposed to a situation. I don’t like to have a situation placed over my head.”
While its entirely unsure what role Murray could have played, it would have been interesting to see him in that scale of movie. Maybe it was a small cameo like he did on Zombieland, or maybe it was something larger like the role of J.A.R.V.I.S. either way, it may never be known what was planned.