The band built their reputation playing clubs in Liverpool and Hamburg over a three-year period from 1960. Manager Brian Epstein moulded them into a professional act and producer George Martin enhanced their musical potential. They gained popularity in the United Kingdom after their first modest hit, "Love Me Do", in late 1962. They acquired the nickname the "Fab Four" as Beatlemania grew in Britain over the following year, and by early 1964 they had become international stars, leading the "British Invasion" of the United States pop market. From 1965 on, the Beatles produced what many critics consider their finest material, including the innovative and widely influential albums.