To many ballet critics, Ms. Seymour was perhaps the greatest dance-actress of her generation, with a fluid, naturalistic style and uncanny ability to disappear into a part. “Above all,” dance critic David Vaughan once wrote, “what makes Seymour so rare and valuable an artist is that both by intuition and intelligence she approaches all dancing in a ‘modern’ way, in the use of the whole body, the ability to convey drama through movement, the sense of commitment.”
Ms. Seymour also taught dance, dabbled in choreography and directed companies in Munich and Athens, including during a stint in the late 1970s at the Bavarian State Opera Ballet. Onstage, she performed in classics such as “Swan Lake” and “The Sleeping Beauty” — “like a good girl should,” she joked — but was happiest in new roles, which gave her a chance to find or create meaning in her steps, rather than learn a series of established movements.
Raised in a patch of rural Alberta that she described as “wheat, oil and cow country,” Ms. Seymour studied dance in Vancouver before coming under the wing of Ashton, a classical choreographer and director known for his work with the Royal Ballet. He turned to Ms. Seymour to originate roles including the lovestruck Young Girl in “The Two Pigeons” (1961), the bored housewife Natalia Petrovna in “A Month in the Country” (1976) and the modern dance pioneer Isadora Duncan, whose earthy, free-flowing technique inspired his solo work “Five Brahms Waltzes in the Manner of Isadora Duncan” (1975-76).
Ms. Seymour was also a muse for MacMillan, who cast the dancer as mysterious, seductive or independent-minded women such as Mary Vetsera in “Mayerling” (1978), about an apparent murder-suicide in 19th-century Vienna, and Anna Anderson, who claimed to be Tsar Nicholas II’s youngest daughter, in “Anastasia,” which premiered as a one-act in 1967 and was later expanded into a full-length ballet.
“We thought we were going somewhere, breaking new ground all the time,” she told the Sunday Times of London in 2017, looking back on her partnership with MacMillan. “Kenneth wanted us to come up with ideas. He filled in the scene like a theater director, then gave us a lot of responsibility in finding our way. … One of the good bits of advice he gave me was, don’t be afraid to be ugly. The other was that you’ve got to find your light, otherwise there’s no point going on.”
For “The Invitation” (1960), one of her first collaborations with MacMillan, she played a young woman who is seduced and raped onstage. The cast included Christopher Gable, with whom she was later selected to star in MacMillan’s “Romeo and Juliet” (1965), a production that featured music from Russian composer Sergei Prokofiev and, with a different lead cast, became a box-office sensation.
The production “broke hearts and shattered my life,” Ms. Seymour recalled.
In her 1984 autobiography, “Lynn,” written with journalist Paul Gardner, she said that during the lead-up to the ballet, she had an abortion so that she could continue rehearsing. “We could have other children, I reasoned. Juliet was mine,” she wrote, adding that the role “was a priceless gift from Kenneth, glazed especially for me. Juliet, the classical heroine of the theater, was the culmination of all my fantasy roles as a dancer.”
But shortly before the premiere, the Royal Ballet’s American impresario, Sol Hurok, pushed for bigger stars. Ms. Seymour and Gable were dropped from the main cast, and the ballet opened with Rudolf Nureyev and prima ballerina Margot Fonteyn, to whom she was forced to teach the steps.
Relegated to the second cast, Ms. Seymour was devastated. Her marriage to dancer-turned-photographer Colin Jones soon collapsed. Yet she also found some of the success she had craved, delivering a raw, sensual performance that enthralled critics and shocked audiences.
“Where other Juliets on the balcony would look longingly up to the stars, she used to writhe like a cat in heat, brushing her arms, shoulders, neck against the balcony itself, her whole body in need of friction,” New York Times dance critic Alastair Macaulay recalled decades later. “‘That’s not Juliet, that’s a whore,’ I remember some fans saying. I was smitten.”
Ms. Seymour returned to the role a few years later, playing Juliet to Mikhail Baryshnikov’s Romeo. She also maintained a friendship with the show’s original male lead, Nureyev, partnering with him on projects that included a 1979 film version of “Giselle.” The Russian dancer was entranced, according to “Nureyev,” a biography by Julie Kavanagh; once, he described Ms. Seymour’s dancing as a kind of artistic aphrodisiac. “Heaven descends into your lap,” he said.
Not all of Ms. Seymour’s fellow dancers were so enamored by her persona.
“I think I was rather foreign,” she told the New York Times in 1989, looking back on her years at the Royal Ballet. “I was essentially sort of North American in what to me was a sort of foreign situation. It was a culture shock. I must have seemed rather abrasive and certainly rather too keen. You had to be cool there, at all costs, which was an art I didn’t have an ounce of.”
As she told it, the act of performance itself was not entirely natural to her. She felt more at home in the privacy of the rehearsal room than facing “the terrifying flood of shimmering white and blue and gold stage lights” at a venue like the Royal Opera House.
“The stage is not magic for me,” she wrote in her autobiography. “I always felt the audience was waiting to see that first drop of blood.”
Berta Lynn Springbett — by her account, it was MacMillan who suggested she change her name — was born in Wainwright, Alberta, on March 8, 1939. Her father was a dentist, her mother a homemaker. She began studying dance after watching the Powell and Pressburger film “The Red Shoes” (1948) and seeing a performance of the ballet “Coppélia,” and at 15 she auditioned for Ashton, who was touring Canada with the Sadler’s Wells Ballet.
Ms. Seymour won a scholarship to study at what is now the Royal Ballet School, and in 1956 she joined the Covent Garden Opera Ballet. She was soon dancing with the Royal Ballet Touring Company, and in 1958 she starred in MacMillan’s “The Burrow,” a claustrophobic drama that reminded some critics of “The Diary of Anne Frank.” The next year, she was named a principal dancer for the Royal Ballet.
Her connection with the company was severed for a few years after the premiere of “Romeo and Juliet,” when she moved to West Berlin to join MacMillan at the Deutsche Oper, working as prima ballerina while he served as director. After MacMillan was given that post at the Royal Ballet in 1970, Ms. Seymour returned to the company as well, this time as a guest artist.
Ms. Seymour worked with a host of choreographers, including Jerome Robbins (“Dances at a Gathering”), Glen Tetley (“Voluntaries”), John Cranko (“Onegin”) and Alvin Ailey, for whom she played a troubled rock star in “Flowers” (1971), inspired by the life of Janis Joplin. She announced her retirement from the stage in 1981.
In part, she was physically exhausted, tired of the toll that dancing took on her body. “I’m not much use for anything the next day — or the day after that,” she told Britain’s Observer newspaper.
Yet she found it difficult to quit entirely, coming out of retirement for roles that included originating the Wicked Stepmother in Matthew Bourne’s “Cinderella,” which premiered in 1997 on London’s West End.
Ms. Seymour’s marriages to Jones, Philip Pace and Vanya Hackel all ended in divorce. Survivors include twin sons from a relationship with Deutsche Oper dancer Eike Waltz, Jerszy and Adrian Seymour; a son from her second marriage, Demian Pace; a brother; and four grandchildren.
For all the intricacies of her footwork, Ms. Seymour confessed that much of the time she could hardly see what she was doing. She was nearsighted, and said she had to memorize the layout of the stage, moving from place to place through a technique that she called “semi-blind Braille.”
When the Times of London asked in 1997 why she didn’t just wear contact lenses during performances, she explained that she “tried them once, but it was a disaster.
“Not only was I able to see the audience, I couldn’t find my balance because they gave me a false sense of where the floor was, so I never wore them again. I found being able to see properly terribly invasive. I prefer to be in my own world, which is far better — and far safer.”