The Oscar win -- the first for 45-year-old Whitaker -- marked the actor's triumphant return to the silver screen after an extended run of behind-the-camera work.

 Whitaker, struggling for words before pulling out a written text, described his Oscar victory as a triumph over his humble beginnings in east Texas and the streets of south-central Los Angeles.

 "When I was a kid, the only way I saw movies was from the backseat of my family's car at the drive-in. And it wasn't my reality to think I would be acting in movies. So, receiving this honor tonight tells me that it's possible," he said.

 "Through our combined belief we can create a new reality," he added, thanking the people of Uganda for their spirit.

  Whitaker beat out Leonardo DiCaprio ("Blood Diamond"), Ryan Gosling ("Half Nelson"), Peter O'Toole ("Venus") and Will Smith ("The Pursuit of Happyness") to take home the coveted statuette.

Earlier Mirren, 61,  in her first Academy Award-winning turn, depicts Queen Elizabeth II as a resolute sovereign, bound by tradition and protocol, who wrestles with public pressure to grieve alongside her nation after Princess Diana's death.

 Long considered the favorite to take home the coveted Oscars statuette, Mirren fought off stiff competition from Penelope Cruz ("Volver"), Meryl Streep ("The Devil Wears Prada") and fellow Britons Judi Dench ("Notes on a Scandal") and Kate Winslet ("Little Children").

 The win completed a clean sweep for Mirren this awards season, after the role garnered her a Screen Actors Guild Award, a Golden Globe and a BAFTA