A sideman is a professional musician who is hired to perform or record with a group of which he is not a regular member. Sidemen are generally required to be adaptable to many different styles of music, and so able to fit smoothly into the group in which they are currently playing. Many sidemen are famous in their own right, however, and may be highly sought-after by bands. Often sidemen go on to form their own groups and/or solo careers; for instance, John Lennon, Paul McCartney, George Harrison, and Pete Best acted as sidemen to Tony Sheridan before becoming famous as The Beatles.