Rebecca Hall has admitted she was "overwhelmed" at the thought of working with Robert Downey Junior on Iron Man 3.
The Vicky Cristina Barcelona actress said she felt nervous before starting work on the Marvel action film together but that Robert, who plays Tony Stark, put her at ease.
Rebecca, who plays scientist Maya Hansen in the movie, said: "[Robert] is a force of nature, no one has had the trajectory he has had."
Robert, 48, takes the lead role as a troubled man who uses his iron suits to overcome his difficulties.
Rebecca, 30, said: "He is Tony Stark - he went through all that, came back, and has this astonishing personality. It is overwhelming before you meet him but I think he's been around long enough to know people are likely to be intimidated by him, so he has a very clever way of being warm and interested in other people that puts everyone at their ease."
The actress, whose partner is director Sam Mendes, thinks Robert's way of dealing with people is behind Iron Man's success.
She said: "The franchise would never have worked if he was a superstar on a perch not deigning to come down and talk to anyone.
"He spars with people he works with and gets excited about actors and they get excited about him. His whole way of doing everything is very intoxicating and contagious.
"It's as fun to make as it is to watch him doing that stuff."