But Plummer and his career aren't mired in the past. Slipping easily from one disparate recent role to another, he's created Leo Tolstoy in "The Last Station," the haunted magnate in "The Girl With the Dragon Tattoo" and a man experiencing a late-in-life gay awakening in "Beginners," which earned him an Oscar last year at age 82.
That made him the oldest acting honoree ever, and he's not stopping. He plays a U.S. Supreme Court justice in HBO's "Muhammad Ali's Greatest Fight," debuting at 8 p.m. Saturday, a history-textured film that puts the boxer's quest to be recognized as a conscientious objector against Vietnam War service and the high court in the ring.
"I don't think retirement exists in our profession," said Plummer, looking every bit the star in elegant slacks and jacket, his white hair perfectly groomed.
"If you retire, something's gone very wrong with your career is my theory. Also, why would you want to retire? It's fun to be in this weird, old, ancient, ancient profession."
The Canadian-born Plummer heads the HBO film as John Harlan II, who was among the justices who decided in 1971 whether Ali's conviction for refusing to be drafted because of his Muslim-based objections should be upheld or overturned.
The dynamic Ali is represented by the legend himself through news clips woven effectively into the drama. But the emphasis is on the camaraderie and give-and-take among the justices, including Frank Langella as Chief Justice Warren Burger and Danny Glover as Thurgood Marshall, the sole black justice.
Stephen Frears, an Oscar nominee for "The Queen," directed, and the script is by Shawn Slovo ("A World Apart"). The film is based on the book of the same name by Howard Bingham and Max Wallace, with additional research by Slovo.
The story resonated with Plummer because of Ali's anti-war stance -- "As he says, 'Why should I fight them (the Vietnamese)? No one over there has called me (the N-word),'" Plummer said, quoting Ali -- and Harlan's intellectual metamorphosis.
His law clerk, a composite character played by Benjamin Walker ("Abraham Lincoln: Vampire Hunter" and Broadway's "Inherit the Wind"), persuades him to take a second look at the case after it appears settled.
"One man, because he listened to somebody else, was intelligent and vulnerable enough to change his beliefs. That's hugely dramatic to me," Plummer said.
The cast members, mostly stage-trained actors including Fritz Weaver as Justice Hugo Black, were a joy, Plummer said: "We did feel like a club, the old boys' club."
Also a boon was the chance to work with Frears. He compared him to another famed filmmaker, John Huston, who directed Plummer, Sean Connery and Michael Caine in 1975's "The Man Who Would Be King."
Although Plummer is part of a very exclusive club whose members each have won Oscar, Emmy and Tony awards, he declines to pick out his most satisfying performance.
"None of them," he responds quickly. "I always feel I can be a hundred times better."
Even in the case of an Oscar-winning role?
"Yes, of course, God, yes," Plummer said. "I can go on forever talking about other people's films. But not necessarily mine."
"Muhammad Ali's Greatest Fight" debuts at 8 p.m. Saturday on HBO.
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