Tributes have been paid from around the world to Olivia Newton-John, who has died from cancer aged 73. The Grammy-winning superstar reigned on pop, country, adult contemporary and dance charts with a string of hits and won countless hearts as everyone’s favorite Sandy in the blockbuster film version of “Grease”, one of the most successful film musicals ever made. The British-born Australian singer and actress died peacefully at her California ranch surrounded by family and friends on Monday, John Easterling, her husband, wrote on Instagram and Facebook. “We ask that everyone please respect the family’s privacy during this very difficult time,” the message said. Her Grease co-star John Travolta said she "made all of our lives so much better" while its director said: "What you see is what you get with her." An actress and musician, Newton-John achieved commercial success as a country singer and sold millions of records globally. But it was her role as high school student Sandy in the film Grease that catapulted her to worldwide fame. The musical was the biggest box-office hit of 1978, and gave Newton-John three huge hit singles, including You"re The One That I Want and Summer Nights, both performed with co-star John Travolta. And it was a catalyst for change in both her image and her musical direction — shedding her innocent, country-pop image. For a decade from 1973 to 1983, Newton-John was among the world’s most popular entertainers. She had 14 top 10 singles just in the US alone, won four Grammys, starred with Travolta in “Grease” and with Gene Kelly in “Xanadu.” The fast-stepping Travolta-Newton-John duet, “You’re the One That I Want,” was one of the era’s biggest songs and has sold more than 15 million copies. “Physical,” the bouncy, R-rated smash released in 1981, was number one for 10 weeks and was named Billboard’s song of the year despite being banned by some radio stations. An aerobics-friendly promotional clip, filmed in the early years of MTV, won a Grammy for best video. Both musically and image-wise, she reinvented herself during those years. She had a few hits after “Physical,” but her career declined and Newton-John became more likely to make news because of her private life. In 1992, as she was preparing a concert tour, her father died and she was diagnosed with breast cancer. Her marriage to actor Matt Lattanzi, with whom she had a daughter, actor-singer Chloe Lattanzi, broke up in 1995 and a years-long relationship with cameraman Patrick McDermott ended mysteriously. McDermott went missing during a 2005 fishing trip in California and his fate remained unknown years later. Numerous reports alleged that he was living in Mexico, with a new girlfriend. Newton-John married John Easterling, founder of the Amazon Herb Company, in 2008. She was involved in numerous charitable causes, serving as goodwill ambassador for the United Nations Environment Programme and as national spokeswoman for the Children’s Health Environmental Coalition. She also founded the Olivia Newton-John Cancer and Wellness Centre in Melbourne, Australia. Newton-John was the daughter of German literature professor Brin Newton-John and Irene Bron, whose father was Nobel Prize-winning physicist Max Bron. The Newton-Johns moved to Australia when Olivia was 5, but she returned to England in her teens and lived with her mother after her parents broke up. Following the news of her death, scores of fans as well as famous figures from the world of entertainment began to share heartfelt messages and memories. Actress Stockard Channing - who played Rizzo in Grease - said: "I don"t know if I"ve known a lovelier human being. "Olivia was the essence of summer - her sunniness, her warmth and her grace are what always come to mind when I think of her. I will miss her enormously." Singer Rod Stewart called her "the perfect lady, gorgeous, with great poise and with a certain Aussie sophistication". US television host Oprah Winfrey said her "positivity was just infectious". "You"ll be missed, Olivia," she wrote. "Here"s to the good times." Travolta wrote on Instagram: "Your impact was incredible. I love you so much. We will see you down the road and we will all be together again." The film"s director Randal Kleiser said he had been friends with Newton-John for 40 years and "she never changed, she was always exactly the way everyone imagines her". "She was charming, lovely, warm... There are so many clichés you can say about her but in her case it was all true." Asked what his everlasting memory of her will be, he told BBC Radio 5 Live: "Hanging out with her at her ranch. Seeing the real Olivia which was exactly like the Olivia she projected. No cameras around, no people around... she was exactly the same and as loving as ever." Other tributes came from singers Kylie Minogue, who called her an inspiration, and Dionne Warwick who called Newton-John "one of the nicest people I had the pleasure of recording and performing with". Newton-John was first diagnosed with cancer in 1992 and went on to become a leading advocate for cancer research. Her charity, the Olivia Newton John Foundation, has raised millions of pounds to support research. In a statement, the hospital that runs the Olivia Newton-John Cancer Wellness and Research CenteR in Melbourne — which was opened after the star"s campaigning — said she "encouraged, inspired and supported" staff and patients everyday. "We are incredibly grateful for the special relationship we had with Olivia for many years. Her generous support and gift provided hope and changed the lives of thousands of cancer patients... She was the light at the end of the tunnel for many, many people." Her efforts in the field were recogniZed by Queen Elizabeth, who honoured her with a damehood in 2020 New Year"s Honours list. In a statement posted to her social media channels, Newton-John"s husband John Easterling hailed her as "a symbol of triumphs and hope for over 30 years sharing her journey with breast cancer". "Her healing inspiration and pioneering experience with plant medicine continues with the Olivia Newton-John Foundation Fund, dedicated to researching plant medicine and cancer." Newton-John is survived by her husband; daughter Chloe Lattanzi; sister Sarah Newton-John; brother Toby Newton-John; and several nieces and nephews. — Agencies