Olivia Newton-John and Cliff Richard are renowned British-Australian pop singers who gained prominence in the late 20th century. Newton-John, known for her pop and country music style, rose to international fame with hits such as "Physical" and her role in the musical film "Grease." Cliff Richard, on the other hand, is often referred to as Britain's answer to Elvis Presley, having a career spanning over six decades with hits like "Summer Holiday" and "We Don't Talk Anymore." Both artists have significantly influenced popular music, demonstrating longevity and adaptability in their careers.