After drum lessons in his teens, Riel started playing with local trad jazz bands in the 50s. He soon moved on to modern jazz and became the house drummer at the Montmatre Jazzhus, Copenhagen (1963-65). He spent a short time at the Berklee College Of Music in 1966. Although he was playing with Danish Radiojazzgruppen (1965-68), he had become very committed to free jazz and worked with saxophonists John Tchicai and Archie Shepp and bass player Gary Peacock. He formed a quintet with Palle Mikkelborg, which won first prize at the Montreux International Jazz Festival (1968), and then played Newport. Meanwhile, he was playing with rock group Savage Roses (1968-72). In the 70s he co-led a group called V8 with Mikkelborg and has since freelanced throughout Europe.