This guy was an art school buddy of John Lennon. He joined the group in 1960 as a bassist, even though he could not play. After selling one of his paintings,he had the money to upgrade their equipment. Actually, he is one of several people sometimes referred to as the "Fifth Beatle". Stu experienced severe headaches and died at the age of 21 because of the cerebral haemorrhage.

More Info: en.wikipedia.org