Olivia Newton-John, who sang some of the biggest hits of the 1970s and ’80s while recasting her image as the virginal girl next door into a spandex-clad vixen — a transformation reflected in miniature by her starring role in “Grease,” one of the most popular movie musicals of its era — died on Monday at her ranch in Southern California.

For years she was a prominent advocate for cancer research, starting a foundation in her name to support it and opening a research and wellness center in metropolitan Melbourne, Australia.

Newton-John beguiled listeners with a high, supple, vibrato-warmed voice that paired amiably with the kind of swooning middle-of-the-road pop that, in the mid-1970s, often passed for country music.

“Grease” became one of the highest grossing movie musicals ever, besting even “The Sound of Music.” Its soundtrack was the second best-selling album of the year, beaten only by the soundtrack for “Saturday Night Fever,” which also starred Mr.

(The other No. 1 single from the “Grease” soundtrack was the title song, sung by Frankie Valli.) A ballad Ms.

Newton-John sang alone, “Hopelessly Devoted to You,” earned the film’s lone Oscar nomination, for best song.

Newton-John titled her next album “Totally Hot,” and presented herself on the cover in shoulder-to-toe leather.

The album, released at the end of 1978, went platinum, yielding the rock-oriented “A Little More Love” with the line, “Where did my innocence go?”.

Olivia Newton-John was born on Sept.

26, 1948, in Cambridge, England, the youngest of three children of Brinley and Irene (Born) Newton-John.

While tarrying there, she recorded her first single, “’Til You Say You’ll Be Mine,” which Decca Records released in 1966.

Following his grand design, the group starred in a science-fiction film written for them and recorded its soundtrack.

Her debut solo album, “If Not for You,” was released in 1971, its title track a cover of a Bob Dylan song.

Newton-John released the album “Let Me Be There” (1973), which led to a Grammy win for best female country vocal performance.

Two key changes in pop music boosted her career that decade: the rise of “soft rock” in reaction to the harder genres of the late 1960s, and the mainstreaming — some would say the neutering — of country music, also epitomized by stars like John Denver and Anne Murray.

Newton-John was chosen female vocalist of the year by the Country Music Association over more traditional stars like Loretta Lynn and Dolly Parton.

Newton-John recorded her “Don’t Stop Believin’,” album in Nashville in 1976, the friction eased.

While the movie floundered, its soundtrack went double-platinum, boasting hits like “Magic” (which commanded Billboard’s No. 1 spot for four weeks) and the title song, recorded with the Electric Light Orchestra.

Travolta in the 1983 movie “Two of a Kind,” an attempt to repeat the success of “Grease.” But the film disappointed even as its soundtrack proved popular, especially the song “Twist of Fate.”.

In addition to her husband, she is survived by her daughter, Chloe Rose Lattanzi; her sister, Sarah Newton-John; and her brother, Toby.

Her Olivia Newton-John Foundation Fund is dedicated to researching plant-based treatments for cancer, and she opened a cancer research and wellness facility under her name at Austin Hospital, outside Melbourne.

Newton-John firmly believed in her audience-friendly approach to music