Stuart Sutcliffe was an early member of the Beatles, joining the band in 1960. He played bass guitar and was a friend of John Lennon from their school days. Sutcliffe left the band in 1961 to pursue his career as an artist, but he is still remembered as an important part of the early Beatles. His nickname was 'Stu' which is why it is used as the three letter answer for this crossword puzzle.