Sir George Henry Martin (3 January 1926 – 8 March 2016) was an English record producer, arranger, composer, conductor, and musician. He was commonly referred to as the "fifth Beatle" because of his extensive involvement in each of the Beatles' original albums. Martin's formal musical expertise and interest in novel recording practices facilitated the group's rudimentary musical education and desire for new musical sounds to record. Most of their orchestral and string arrangements were written by Martin, and he played piano or keyboards on a number of their records.
https://en.wikipedia.org/wiki/George_Martin