Day 18: 1946.

Going from the beginning of the first world war to a year after the second, it is safe to say that this song is probably the most famous and even the most played carol to come out of the 20th century. Especially with the singer, Nat King Cole, that if there's anything of his legacy that he's being remembered, it would be this very tune. He sang this on TV in 1961, but the way he sang it is considered by many the most perfect version of this song out there. So without further adue ladies and gentlemen: The Christmas Song.