Not the most successful
The Guinness Book of World Records has dubbed Elvis Presley the best selling solo artist with 110 gold discs, 50 platinum, and 25 multi-platinum. His sales are estimated in the billions, with over 200 million RIAA certified sales. The source for McCartney's 60 gold disc being the greatest is heavily outdated, and needs to be reprised. All my evidence can be found on the Elvis Presley Discography reference page, within the first 5 sources, same for his main page (albeit, third or fourth paragraph). The well documented best selling recording artists article on here also has everything cited, in which Presley's sales and success highly overshadows Paul. Not only him, but the likes of Elton John and Michael Jackson have also out shined him. While his song writing basis is certainly acceptable, the claim of the most successful is asinine.