"Let It Be" is a song written by Paul McCartney (although credited to Lennon/McCartney), and released by The Beatles as a single in March 1970, as the title track of their album, Let It Be.
The song was inspired by McCartney's mother, Mary McCartney (who was deceased), after he dreamt about her saying the words, "let it be."
The single reached #1 in the U.S. and #2 in the UK. The single also peaked at #1 at the charts in Australia, Norway and Switzerland. In 2004, it was ranked number 20 on Rolling Stone magazine's list of the 500 greatest songs of all time.
After the hundred or so times I've heard this, I think it's probably Ringo's drumming that I like the most. Here is the performance from the film, Let It Be:
My mother always whispers, "Letter B."
And I can't hear it without thinking for at least a second about The Beetles' performance of their version on a 1979 episode of Sesame Street: