The singularity of opera star Hildegard Behrens' life was summed up by the circumstances of her death.

At age 72, well past typical soprano retirement age, Ms. Behrens had been planning a recital and master class in Japan when, feeling unwell, she checked into a hospital Sunday, suffering from an aneurysm from which she died Tuesday.

No doubt she grieved over canceling. "I'm a long-distance singer," she told The Inquirer six years ago. "The longer the better."

Ms. Behrens was widely considered the most magnetic Wagnerian soprano of her time - not just for her singing, but for her acting as well - and enjoyed a stable family life in Washington, where she lived for many years with her husband and two children. Even during periods of ill health following a 1990 onstage accident, she insisted on continuing to sing. When she arrived for her 1982 Philadelphia Orchestra debut and discovered she was slated to sing an aria she had long since forgotten, Mozart's "Come scoglio," she relearned it and sang the program as advertised. When she was no longer hired to sing Wagner's challenging "Immolation Scene" in the world's opera houses, she sang it in recital halls, among them the Kimmel Center's Perelman Theater in 2003, with success.

Ms. Behrens filled a considerable void in the late-1970s international opera scene as Birgit Nilsson was winding down her career with no clear-cut successor. Gwyneth Jones was having periods of uneven vocalism following a car accident; Roberta Knie was stymied by Metropolitan Opera politics.

Though Ms. Behrens earned a law degree at the University of Freiburg, in deference to her parents, she studied voice and theater all along. She was discovered at the mature age of 40 in her native Germany, during a run of Wozzeck in Dusseldorf, by the career-making conductor Herbert von Karajan. He immediately hired her to sing in his 1977 production of Salome in Salzburg for reasons that set the tone for her international career: She sang dramatic roles without a pile-driver voice, cut a handsome figure onstage, and knew how to project a characterization without even opening her mouth.

Customarily, Karajan recorded operas in Vienna prior to going into production in Salzburg, using the recordings during stage rehearsals to keep singers from wearing down their voices. But he was so intent on springing Ms. Behrens on the world that he made her lip-synch to an older Birgit Nilsson recording. Ms. Behrens was a sensation; her Salome recording is still considered the best of its kind.

She went on to become a conductor's singer, perhaps because she wasn't cowed by them. She argued bitterly with Karajan when he insisted that a dancer - not her - perform Salome's dance of the seven veils. When recording Fidelio with Sir Georg Solti, the conductor told her not to be intimidated by him, to which she replied, "Maestro, I'm not afraid of you. I'm afraid of Beethoven." Leonard Bernstein was so besotted with her talent after their Tristan und Isolde recording, he was seen in the audience at her Metropolitan Opera opening nights.

Ms. Behrens' Met career began with ill-fitting Puccini roles, specifically Il Tabarro and Tosca. The Behrens voice never pretended to have the luster of more Italianate singers, though the theatricality she brought to Puccini was rarely equaled. What's often a point of audience indulgence for chubby divas in Tosca was a Behrens high point: When her character jumps to her death from the fortress walls, Behrens appeared to literally embrace death with arms outstretched in a visual image that seemed both spontaneous and sculptural.

Not until the Met's four-part, 16-hour Ring cycle, which was unrolled in the mid-1980s, was Ms. Behrens' reputation consolidated with complete recordings of the saga and nationally televised videos. In that last medium, she became the human face of Wagner. The Otto Schenk production was a model of unfussy, pastoral realism, to which she brought an added humanity, often in camera close-ups in which she didn't even sing. But in her periodic opera-in-concert performances with the Boston Symphony Orchestra - playing Elektra both in the Richard Strauss opera of the same name and in Mozart's Idomeneo - she needed no scenery to create her character's world.

During her 1980s vocal prime, however, Ms. Behrens sang performances that left listeners concluding her voice was shot; days later, she would emerge fresher and more brilliant than ever. Such vocal lapses became more than momentary, however, after 1990, when she was injured by moving scenery at the conclusion of a Met Gotterdammerung performance being taped for television.

At first, her injuries were said to be minor; the telecast was salvaged by video from rehearsals. In fact, Ms. Behrens had been knocked unconscious, leaving her with black eyes and back injuries. She became a vegetarian to lose weight and take pressure off her spine, but didn't stop singing, even though she later admitted to giving performances she wasn't proud of.

"I couldn't stop," she said. "Otherwise, I would never have been able to pick it up again. But it's terrible when the [vocal] machine doesn't work. Dreadful." Later roles included Ortrud in Lohengrin, Kostelnicka in Jenufa.

Though the younger Ms. Behrens often seemed ill at ease offstage, she eventually responded to her star status with warm, attentive interactions with her admirers, even when strangers. A chance encounter with her on a Salzburg stairway could yield a detailed explication of the Luciano Berio opera she was premiering in the coming months.

News of her death prompted a degree of affection unusual even for opera fans. "I will never forget the way that she embraced Wotan during the final scene," read one anonymous post on Operadepot.com. "It wasn't as a valiant Valkyrie but as an awkward teenager daughter. . . . It was one of the most moving moments I have ever experienced in opera."

Contact music critic David Patrick Stearns at dstearns@phillynews.com