Well-versed Beatles aficionados will know that today is the 44th anniversary of Paul's "death." The infamous urban legend goes as follows: During the wee hours of November 9th, 1966, Paul McCartney was involved in a car accident; he died, tragically, from the injuries he sustained. The Beatles then conspired to deceive the public on a grand scale by replacing Paul with an unimaginably similar (and talented) impostor. In their music, artwork, and elsewhere, they planted clues about this ongoing act of perfidy. Only through the diligent efforts of very clever and perceptive fans was the plot eventually uncovered. To no surprise, the official response from The Beatles and their handlers was always one of denial.
This is the "Paul is dead" hoax in a nutshell. I've explored the topic a fair amount in the past, so I don't feel the need to go further at the moment. I'll restrict myself to two comments. 1) I wrote this two summers ago (see the third link), and it unfortunately holds true: "...the more I read about the "Paul-is-Dead" hoax, the less intrigued I become." 2) One aspect of it that continues to fascinate me is its murky origin. No one knows precisely how the notion came into being, which adds mystery to an already thickly mysterious (though patently preposterous) farrago of theories.