George Martin - "Paul always took inspiration from John, especially in his lyric writing. ‘Eleanor Rigby,’ for example, wouldn’t have happened without John’s influence. Paul wrote all of it, but John’s influence was there and similarly John was knocked out by the freshness Paul brought to melodies and harmonies. He learnt from Paul how to put in the odd chord that choked you up a bit.” (MOJO 2007)
Richard Starkey aka Ringo Starr - the quiet Beatle. He rounded off the group nicely and, being laid back, didn't challenge the talents of the main writers. When he did sing a song, however, it was typically very Ringo, due to his extremely recognisable voice. See "Boys", "With a Little Help From My Friends" and "Yellow Submarine" for good examples.