A veteran performer in Germany and his native Austria, Waltz had been a virtual unknown in Hollywood when Tarantino cast him as a gleefully evil Nazi in 2009's "Inglourious Basterds," which won him his first Oscar.
"I have to cast the right people to make those characters come alive," said Tarantino, who won previously for "Pulp Fiction. "And boy, this time, did I do it. Thank you so much, guys."
Waltz has since done a handful of other Hollywood movies, but it's Tarantino who has given him his two choicest roles. Backstage, Waltz had a simple explanation for why the collaboration works.
"Quentin writes poetry, and I like poetry," Waltz said.
Oscar host Seth MacFarlane opened with a mildly edgy monologue that offered the usual polite jabs at the academy, the stars and the industry. He took a poke at academy voters over the snub of Ben Affleck, who missed out on a directing nomination for best-picture favorite "Argo," a thriller about the CIA's plot to rescue six Americans during the Iranian hostage crisis.
"The story was so top secret that the film's director is unknown to the academy," MacFarlane said. "They know they screwed up. Ben, it's not your fault."
"Argo" also claimed the Oscar for adapted screenplay for Chris Terrio, who worked with Affleck to create a liberally embellished story based on an article about the rescue and part of CIA operative Tony Mendez's memoir.
Terrio dedicated the award to Mendez, saying "33 years ago, Tony, using nothing but his creativity and his intelligence, Tony got six people out of a bad situation."
The foreign-language prize went to Austrian filmmaker Michael Haneke's old-age love story "Amour," which had been a major surprise with five nominations, including picture, director and original screenplay for Haneke and best actress for Emmanuelle Riva, who turned 86 on Sunday and would be the oldest acting winner ever.
The top prize winner at last year's Cannes Film Festival, "Amour" follows the agonizing story of an elderly man (Jean-Louis Trintignant) tending his wife (Riva) as she declines from age and illness.
Haneke thanked his own wife for supporting him in his work for 30 years.
"You are the center of my life," Haneke said.
The Scottish adventure "Brave," from Disney's Pixar Animation unit, was named best animated feature. Pixar films have won seven of the 12 Oscars since the category was added.
"I just happen to be wearing the kilt," said "Brave" co-director Mark Andrews, who took the stage in his trademark Scottish garment.
The upbeat musical portrait "Searching for Sugar Man" took the documentary feature prize. The film follows the quest of two South African fans to discover the fate of acclaimed but obscure singer-songwriter Sixto Rodriguez, who dropped out of sight after two albums in the 1970s and was rumored to have died a bitter death.
"Thanks to one of the greatest singers ever, Rodriguez," said "Sugar Man" director Malik Bendjelloul.
There was a rare tie in one category, with the Osama bin Laden thriller "Zero Dark Thirty" and the James Bond tale "Skyfall" each winning for sound editing.
William Shatner made a guest appearance as his "Star Trek" character Capt. James Kirk, appearing on a giant screen above the stage during MacFarlane's monologue, saying he came back in time to stop the host from ruining the Oscars.
"Your jokes are tasteless and inappropriate, and everyone ends up hating you," said Shatner, who revealed a headline supposedly from the next day's newspaper that read, "Seth MacFarlane worst Oscar host ever."
The performance-heavy Oscars also included an opening number featuring Charlize Theron and Channing Tatum, who did a classy dance while MacFarlane crooned "The Way You Look Tonight." Daniel Radcliffe and Joseph Gordon-Levitt then joined MacFarlane for an elegant musical rendition of "High Hopes."
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