Robert Downey Jr. felt "trepidation" before the birth of his son.

The Hollywood actor and his wife Susan Levin welcomed Exton Elias into the world in February.

Robert who also has an 18-year-old son Indio from a previous relationship admits he was wracked with nerves before Exton was born. However, since the baby arrived Robert has relaxed into his parenting duties.

"There was all this trepidation, all this projection, all this anticipation and goodwill and a good vibe about it. But what you're squeezing to the side or what's in the glove box is these thousands of forms of fear," he told the latest US edition of Esquire. "And then he was born and they've all just kind of scattered now. It seems like he's always been here.

"Am I going to know what to do with them? Does any new parent, even if you're not a first-time parent, ever really know what to do? Only thing you have to do, the only requirement, if you can hack it, is to not transfer your own discomfort in the moment to this fresh soul, right? You got to be mindful."

Robert also revealed that he wants his new-born son to see him as a real person rather than put him on a pedestal.

Although the 47-year-old star is well known for playing superhero Iron Man, he hopes his son will realise he makes mistakes just like everyone else.

"Do I want to be a hero to my son? No. I would like to be a very real human being," he explained. "That's hard enough. Every dad casts a shadow, you know? And that shadow is you're disappointed, you're resentful, or you feel so supported and loved you don't understand why life is so hard anyway or, you know, it's so long and so dark that you can never step out of it, so you might as well not even try. Right? So. So hero to me is not applicable to the human experience.

"I think that we all do heroic things, but hero is not a noun, it's a verb."