In a year of strong male roles, Hoffman was the overwhelming favorite. His portrayal of Truman Capote during the years the author was researching and writing "In Cold Blood" has been universally hailed as a triumph of transformation. He already had won the Golden Globe, Independent Spirit and Screen Actors Guild awards, as well as top honors from critics groups across the country.
Hoffman was up against a tough field, including two other actors who gave evocative performances of iconic figures: Joaquin Phoenix as Johnny Cash in "Walk the Line" and David Strathairn as Edward R. Murrow in "Good Night, and Good Luck."
Also in the running were Heath Ledger as a cowboy tormented by his gay love affair in "Brokeback Mountain" and Terrence Howard as a pimp with dreams of rap stardom in "Hustle & Flow."
Take Hoffman out of the race and one of them could have taken home the trophy. But he captured the author's voice, carriage and mannerisms so completely, without ever lapsing into caricature, that he made you forget you were watching an actor playing a role.
The Academy Award comes after years of building a career on daring and often difficult supporting parts, including the porn-star hanger-on in "Boogie Nights," the scheming dandy in "The Talented Mr. Ripley" and the obscene phone caller in "Happiness." He's proven he's equally adept at comedy, playing rock journalist Lester Bangs in "Almost Famous," a drag queen in "Flawless" and a former child star in "Along Came Polly."
George Clooney won the supporting-actor Academy Award on Sunday for the oil-industry thriller "Syriana," and Rachel Weisz took the supporting-actress prize for another corporate thriller, "The Constant Gardener."
The win capped a remarkable year for Clooney, who made Oscar history by becoming the first person nominated for acting in one movie and directing another.
Along with performing in "Syriana," Clooney directed the Edward R. Murrow tale "Good Night, and Good Luck," which earned him directing and writing nominations and was among the best-picture contenders.
In "Syriana," Clooney effaced his glamour-boy looks behind the bearded, heavyset facade of a CIA patriot who grows jaded over U.S. oil policy in the Middle East.
"All right, so I'm not winning director," Clooney joked, adding that an Oscar win always would be synonymous with his name from then on, including in his obituary. "Oscar winner George Clooney, sexiest man alive 1997, `Batman,' died today in a freak accident."
Clooney also lauded Oscar voters for their daring.
"This group of people gave Hattie McDaniel an Oscar in 1939 when blacks were still sitting in the back of theaters," Clooney said, referring to the supporting-actress winner from "Gone With the Wind," the first black performer to receive an Oscar.
In "The Constant Gardener," adapted from John le Carre's novel, Weisz played a humanitarian-aid worker whose fearless efforts against questionable pharmaceutical practices makes her a target for government and corporate interests in Africa.
Weisz thanked co-star Ralph Fiennes and director Fernando Meirelles, "and of course, John le Carre, who wrote this unflinching, angry story. And he really paid tribute to the people who are willing to risk their own lives to fight injustice. They're greater men and women than I."