Sir George Martin, CBE (3 January 1926 – 8 March 2016) was an English record producer, arranger, composer, conductor, audio engineer, and musician. He was referred to as the "Fifth Beatle" in reference to his extensive involvement on each of the Beatles' original albums. Paul McCartney said upon Martin's death, "If anyone earned the title of the fifth Beatle, it was George".
George was I believe responsible for the suggestion of the introductory chord at the beginning of Hard Days Night
The chord was confirmed by George Harrison as an Fadd9 during an online chat on 15 February 2001: