Dufek and Antonín Hájek founded The Rangers in 1964. The band was renamed Plavci (Swimmers) in 1971 due to concerns about sharing its name with "American killers in Vietnam" (the United States Army Rangers). Band member Radek Tomášek left Plavci in 1973 due to rivalry with Dufek. The band's name reverted to Rangers in 1989.
Dufek was the composer of several successful songs. He founded the Nadace Dětské Srdce (Children's Heart Foundation) to support treatment for pediatric heart defects.