Robert Downey Jr. has had a "glorious time" playing the villain in Avengers: Doomsday.

The 61-year-old actor is best known for his portrayal of Tony Stark/Iron Man - who died in Avengers: Endgame - in the Marvel Cinematic Universe (MCU), but he's returning to the franchise as Victor Von Doom in Avengers: Doomsday, and he's opened up about the moment it sunk in for him that he's occupying a very different space in the comic book world now.

He told Empire magazine: "Remember Michael Douglas at the end of Falling Down? He goes, 'I'm the bad guy?' I had that realization a couple of days into shooting.

"Because all the heroes are over there, and I'm the problem. And then I leaned in, and it was just this glorious time."

And Downey teased his character's antics will be far more outlandish than audiences are expecting.

He said: "I like a bit of scorched earth. Whatever you think he may be entertaining, I would ten times it, and you'll probably be closer to the ballpark."

Directors Joe and Anthony Russo teased Avengers: Doomsday is a "very scary movie" because of Downey's "very dark" villain.

Joe said: "Doom is a Gothic character. He says, 'Hell answers to me,' and he's not kidding. He's a very powerful character with some very dark magic, and he's not above selling his soul to get what he wants. He's worth being scared of.

"He's a father who's a victim of trauma. He has lost a child. When people see the film they say it's a very scary movie. It's scary because he's so profoundly damaged."

Anthony added: "Doom is much more ego-driven than Thanos. Thanos believed he was serving a greater good."

Fans have queried whether Doom is some sort of variant of Tony Stark, but Marvel boss Kevin Feige has insisted that isn't the case, pointing out Downey isn't the first actor to play more than one character in the MCU because Chris Evans has done the same.

He said: "Is Steve Rogers a Johnny Storm variant? People wondered, 'Is Doom just a variant of another character? Is this just a shortcut to bringing back another character?' The answer is no. He's Victor Von Doom."

The directors previously revealed Downey came up with his distinctive new accent for Victor Von Doom without any input from them.

Anthony told People magazine: "That was something that Robert surprised us with one day. You know, we were talking about all the details of the character -- the voice, of course, is a key part of it, especially in the mask.

"So one day I think it was in the trailer, we were just sort of talking about some ideas and he broke out into the voice. And we knew at that moment, that was it."