For my money, Bob Dylan is far and away the greatest songwriter of the recorded music era. Many people will disagree and it was only about 10 years ago, when I started buying his albums and really exploring and listening to those albums that I started to recognise just how good he is.
Over a period of 50 years, he has written and recorded so many truly great songs and even many of the "lesser" albums are invariably interesting and original.
Much of his best work is little known unless you are a fan and while it is almost impossible to pick out one song from the literally hundreds he has written over the years, if I had to choose a personal favourite it would be "Blind Willie McTell", which was originally rejected from the album it was intended for and only later released as part of the Bootleg series, which again is typical Dylan.
Happy birthday indeed.