Meet Robert: the new biggest movie star in the world

Avengers Assemble is the biggest superhero film of all time, uniting Captain America, Hulk, Thor, Hawkeye, Black Widow and Iron Man, along with Nick Fury and the scheming Loki. They're played by some of Hollywood's hottest talents including Scarlett Johansson, Chris Evans and Samuel L Jackson, who's technically one of the most bankable stars in the business.

And yet who steals every scene he's in during this world-saving action epic? Yep, it's the quick-witted, charismatic, eye-twinkling Robert Downey Jr., who can handle action as readily as the quips and the quivers. And without his terrific turn in Iron Man, Avengers Assemble might never have happened. Box office experts partly credit Downey Jr with the franchise's success, much as Johnny Depp brought his magic to Pirates of the Caribbean.

Avengers Assemble review
Pics: Avengers Assemble premiere in London

Just as Pirates wouldn't have been the same without Depp, Iron Man would have been a very different proposition in more traditional action-hero hands. It seems the world was ready for a renegade, rebellious superhero and Robert Downey Jr's Iron Man was it.

As we all know, it wasn't always thus. Rob has had a chequered career that saw both audiences and industry bods writing him off in the 90s. The son of a director, Downey enjoyed supporting roles in 80s hits like Weird Science but his turn as a drug-addicted student in Less Than Zero boosted both his career and his burgeoning drug habit. "Until that movie I took my drugs after work and on the weekends. That changed on Less Than Zero," he's since said.

Downey managed to keep his vices at bay long enough to gain an Oscar nomination for the biopic Chaplin but he landed in jail in the late 90s. Ironically, it was courtroom drama Ally McBeal that bailed Rob out of obscurity but he was dropped from the show after further drug arrests.

A large part of the noughties was spent trying to clean up his act. Although he scored great reviews with the likes of Kiss Kiss Bang Bang, Good Night and Good Luck and Zodiac, these hardly set the box office on fire.

It was a controversial decision from actor-turned-director Jon Favreau that changed Downey from an increasingly respected has-been to box office gold. "Downey Jr wasn't the most obvious choice but he understood what makes the character tick," says Favreau. It was an inspired move and instantly catapulted Downey Jr to higher echelons of fame. He scored a part in the hilarious Tropic Thunder and the leading role in another irreverent blockbuster: Guy Ritchie's Sherlock Holmes.

Of course, Sherlock Holmes became huge, demanding sequels just like Iron Man. Then the Avengers assembled, casting Downey Jr's Tony Stark as the wise-cracking Alpha male leading a pack of the world's most powerful men and women while wearing a Black Sabbath t-shirt, effortlessly slipping into an iron suit for battle.

Don't get us wrong: Mark Ruffalo for one is a fantastic actor and Tom Hiddleston is going places fast. But can any of the Avengers - or indeed any of Hollywood's hottest - be shooting to the top as quickly as the super-powered, magnetic Downey Jr? If he continues to play his cards right, we doubt it.

Avengers Assemble review
Pics: Avengers Assemble premiere in London