In a field dominated by singers with big or flashy styles, Peggy Lee became a sotto voce legend. The platinum-blond North Dakota native, who died Monday at age 81 from a heart attack, was popular music’s ultimate embodiment of less is more, particularly as aging and ill health took their toll on her voice. With her whispery authority, she conveyed a full range of emotion as powerfully as the fullest-throated divas.

Whether singing pop or jazz or blending them together, the woman who had “Fever” morning and night was the coolest of stylists. Though Miss Lee spent her final years in relative obscurity, recording rarely, her influence can be heard and felt in any number of young singers, including pop chanteuse k.d. lang, genre-mixer Cassandra Wilson and jazz vocalist Jeanie Bryson (Dizzy Gilles-pie’s daughter). An artist who knew the blues and Broadway equally well, she made a habit of defying restrictions and expectations, encouraging women singers to write for themselves by composing such hits as “Manana.”

“You have to have your heart broken at least once to sing a love song,” she once said, quoting Sophie Tucker. But she balanced the pained truth in her vocals with inner strength, revealing a debt to the great Billie Holiday. Those who knew her for fluffy tunes such as her late-’60s hit, “Is That All There Is?,” had to have been surprised by her late emergence as a maker of pointed blues statements. At the advanced age of 68, she garnered a 1989 Grammy Award nomination for her comeback album, “Miss Peggy Lee Sings the Blues.”

Chicago figured prominently in her career. It was at a hotel here that hometown hero Benny Goodman first heard her sing. Hired by the King of Swing in 1941, Miss Lee came close to being fired after she suffered from a case of nerves during her first recording session because she was required to sing in the same key as her predecessor in the orchestra, Helen Forrest. Famed producer John Hammond wanted her gone. Goodman stayed with her and, settling into her own style, she rewarded him with career-defining hits such as “Why Don’t You Do Right?”

After falling in love and marrying Goodman’s guitarist, Dave Barbour (with whom she collaborated as a songwriter and performer), she took a break from singing to raise their daughter, Nicki. When the marriage fell apart, she resumed her career, which began when she was 14 and still known by her given name, Norma Egstrom. A native of Jamestown, N.D., she changed it to Peggy Lee at the suggestion of the program director at the Fargo, N.D., radio station for which she performed.

For all the deep (and generally neglected) rewards of her mature style, her early recordings had a youthful ease and natural sense of swing that are equally hard to resist. Those qualities are on ample display on Mosaic Records’ recently released five-CD set, “The Complete Peggy Lee and June Christy Capitol Transcription Sessions,” consisting of rarities recorded in 1945 and 1946 and intended for radio airplay only.

For all the adversity Miss Lee faced with her multiple marriages, diabetes and heart ailments and occasional artistic misfires — her 1984 one-woman Broadway show, “Peg,” closed after 18 performances — she projected a determined optimism. Even the wrenching theme she wrote for “Johnny Guitar” (1954), Nicholas Ray’s feverish Freudian Western, had an upward spin.

Miss Lee, whose brief acting career included an Oscar-nominated performance in “Pete Kelly’s Blues” (1955), had her own shootouts with the music business. In 1955, she co-wrote music and provided voices for Walt Disney’s “Lady and the Tramp.” More than three decades later, following the videocassette sale of the movie, she sued for a portion of the profits and was awarded $2.3 million by a California court. She had had a clause written into her original Disney contract barring the sale of “transcriptions” of the animated film without her approval.

In addition to her daughter, Nicki Lee Foster, Miss Lee is survived by her grandchildren David Foster, Holly Foster-Wells, and Michael Foster, and three great-grandchildren. Funeral arrangements were pending.