There is a conspiracy theory that claims Paul McCartney died and was replaced by a lookalike in 1966.

'Paul is Dead' was a phrase you could hear if you played the ending of a few Beatles songs. It sparked a conspiracy theory that's still alive today. The real Paul McCartney, the theorists say, died in 1966 and was replaced by a lookalike.

Detailed on the source website, photographic evidence is used to claim he was replaced with a lookalike who underwent plastic surgery. The case is presented very meticulously, focusing on his appearance before and after 1966. 

The first point made is that his face changed very little before 1966. The claim is qualified by comparing two pictures of John Lennon, eleven years apart, and pointing out how identical they are. Two pictures of the allegedly fake Paul McCartney are also compared, and are shown to look identical. Then, "real" Paul McCartney and "fake" Paul McCartney are compared, and it’s pointed out how different they look. 

To establish more credibility, a photo of "fake" Paul McCartney from The White Album poster is juxtaposed with a photo of him in present day, and they are shown to be consistent. The website says that the head shape and size of the "fake" Paul McCartney is all wrong. 

Using pictures of John Lennon’s head to compare, the case is made that McCartney’s head grew, while Lennon’s stayed the same. The claim with possibly the most ground is that the height is different. In a picture of John and Paul performing on the Ed Sullivan show in 1965, the two are shown to be the same height. 

But in the Sgt. Pepper’s Lonely Hearts Club Band pictures, Paul is clearly two to three inches taller than Lennon. Another claim that holds some weight is that his eye color changed. Before 1966, Paul had hazel eyes, according to the website. But today, his eyes are green. The whole conspiracy is dug into very deeply, and makes for a very interesting read. What do you think? Is there any ground to it? 

(Source)