Dame Olivia Newton-John (26 September 1948 – 8 August 2022) was a British and Australian singer and actress. With over 100 million records sold, Newton-John is one of the best-selling music artists of all time, as well as the highest-selling female Australian recording artist of all time.

In 1978, Newton-John starred in the musical film Grease, which was the highest-grossing musical film at the time and whose soundtrack remains one of the world's best-selling albums. It features two major hit duets with co-star John Travolta: "You're the One That I Want"—which is one of the best-selling singles of all time—and "Summer Nights". Her signature solo recordings include the Record of the Year Grammy winner "I Honestly Love You" (1974) and "Physical" (1981)—Billboard's highest-ranking Hot 100 single of the 1980s. Other defining hit singles include "If Not for You" and "Banks of the Ohio" (both 1971), "Let Me Be There" (1973), "If You Love Me (Let Me Know)" (1974), "Have You Never Been Mellow" (1975), "Sam" (1977), "Hopelessly Devoted to You" (1978; also from Grease), "A Little More Love" (1978), "Twist of Fate" (1983) and, from the 1980 film Xanadu, "Magic" and "Xanadu" (with the Electric Light Orchestra).

Newton-John's accolades include four Grammy Awards, a Daytime Emmy Award, nine Billboard Music Awards, six American Music Awards, a star on the Hollywood Walk of Fame and an induction into the ARIA Hall of Fame. She scored fifteen top-ten singles, including five number-one singles on the Billboard Hot 100, and two number-one albums on the Billboard 200: If You Love Me, Let Me Know (1974) and Have You Never Been Mellow (1975). Eleven of her singles (including two Platinum) and fourteen of her albums (including two Platinum and four 2× Platinum) have been certified Gold by the Recording Industry Association of America (RIAA). She was appointed Officer of the Order of Australia in 2006 and Dame Commander of the Order of the British Empire in 2020.

Newton-John, who had breast cancer three times, was an advocate and sponsor for breast cancer research. In 2012, the Olivia Newton-John Cancer & Wellness Centre at the Austin Hospital opened in her home town of Melbourne; in 2015, the facility was rechristened the Olivia Newton-John Cancer Wellness & Research Centre. She was also an activist for environmental and animal rights causes.

Olivia Newton-John was born on 26 September 1948 in Cambridge to Brinley "Brin" Newton-John (1914–1992) and Irene Helene (née Born; 1914–2003). Her father was born and raised in Wales to a middle-class family. Her mother was born and raised in Germany to a German-Jewish academic family who came to the UK in 1933 to escape the Nazi regime.

Newton-John's maternal grandfather was German Jewish Nobel Prize–winning physicist Max Born. Her maternal grandmother Hedwig was the daughter of German Jewish jurist Victor Ehrenberg and his Lutheran wife, Helene Agatha von Jhering. Through Helene Agatha, Newton-John was a descendant of Protestant theologian Martin Luther. She was also descended from an unspecified Spanish monarch. Helene Agatha's own father, Newton-John's great-great-grandfather, was jurist Rudolf von Jhering. Newton-John's uncle was pharmacologist Gustav Victor Rudolf Born. Through her Ehrenberg line, Newton-John was a third cousin of comedian Ben Elton.

Newton-John's father was an MI5 officer on the Enigma project at Bletchley Park who took Rudolf Hess into custody during World War II. After the war, he became the headmaster of the Cambridgeshire High School for Boys and was in this post when Newton-John was born.

In early 1954, when Newton-John was five, her family emigrated to Melbourne, Victoria, on the SS Strathaird. Her father worked as a professor of German and as the master of Ormond College at the University of Melbourne. Her family attended church while her father served as the head of the Presbyterian college.