UPDATE 1-Robert Downey Jr. wins best supporting Oscar for 'Oppenheimer'

(Adds Downey quotes in paragraphs 4-5)

By Dawn Chmielewski

LOS ANGELES, March 10 (Reuters) - Robert Downey Jr. won the Academy Award for best supporting actor for his role in "Oppenheimer," where he played a villainous bureaucrat who seeks to destroy the acclaimed physicist.

Downey played Lewis Strauss, the former chairman of the U.S. Atomic Energy Commission who mounted a behind-the-scenes campaign to strip J. Robert Oppenheimer of his security clearance by tarring him as a communist.

Strauss's efforts were later exposed during a congressional hearing as he sought confirmation to serve as President Dwight Eisenhower's commerce secretary.

The actor thanked his "terrible childhood and the Academy - in that order" and his wife Susan, who he said "found me a snarling rescue pet" and "loved me back to life." He also acknowledged the cast and crew of "Oppenheimer."

"What we do is meaningful," Downey said. "What we decide to do is important."

Critics praised Downey for playing against his conventional type. Though he has played junkies, hustlers and fast-talkers, Downey is perhaps best known for his multiple film appearances as Marvel superhero Iron Man.

Downey was considered a frontrunner for the best supporting actor Oscar, having collected Golden Globe and Screen Actors Guild trophies for his co-starring role.

The actor earned his first Oscar nomination for playing Charlie Chaplin in 1992's "Chaplin." After battles with scandal and addiction, he earned a second supporting-actor nomination for his role in the war satire "Tropic Thunder." (Reporting by Dawn Chmielewski; Editing by Jonathan Oatis

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