Ali G's Oscars appearance was not sanctioned by the Academy

Sacha Baron Cohen, left, appears as Ali G while presenting an Oscar award with Olivia Wilde. Photo/AP

Sacha Baron Cohen resurrected his Ali G alter ego at the Oscars - but his appearance was a complete surprise to organisers.

The 44-year-old actor teamed his tuxedo with his famous white wannabe rapper character's sunglasses and hat and addressed the audience about diversity when he stepped out to present the Best Picture Academy Award with Olivia Wilde, who looked on silently as he spoke in support of "all people of all colours."

He said: "'Ow come there's no Oscar for dem very hard-working little yellow people with tiny dongs - you know, the Minions.

"But I is here representing all of them that's been overlooked. Will Smith. Idris Elba. And of course that amazing black bloke from Star Wars - Darth Vader."

Raising his arm in solidarity, he added: "Dis is for you."

Cohen later told E! his wife, Isla Fisher, helped him sneak his disguise into the ceremony.

"The truth is we actually had to sneak it in, because the Oscars sat me down before and said they didn't want me to do anything out of order, they wanted me to actually just present it as myself," he told Good Morning Britain.

"But luckily my wife put on the Ali G beard in the disabled toilets, and I managed to get away with it."

Cohen initially retired Ali G in 2007, but brought him back briefly in 2012 and again in 2014.

Four years ago, the British star caused a stir when he arrived at the ceremony in his Dictator guise of Admiral General Aladeen and threw ashes over Ryan Seacrest's suit, after telling the presenter he was carrying an urn containing the ashes of deceased North Korean dictator Kim Jong II, whose dream was to be sprinkled over the red carpet.

The E! News host could be seen saying "no" and turning away when he saw Cohen on the red carpet, refusing to interview him.

However, the Grimsby star later interrupted Ryan's interview with Lady Gaga and the two men shared a hug.

- Bang! Showbiz