Elvis could rightfully be called The King. Just not The King of rock and roll. Elvis was a tremendous entertainer, but he was not a rocker by even the most generous of definitions.
Chuck Berry had a lasting influence on rock and roll. A number of famous rocker say that it was Chuck Berry who first impressed them and caused them to become rockers. One of them is Keith Richards. He said that when he first saw Chuck Berry he knew then and there what he wanted to do in life. A number of other famous rockers have said the same thing. With them having been influenced by Chuck Berry they have since influenced many others, all because of the impact Chuck Berry had on them.
Chuck Berry showed a tremendous amount of talent, he was a pioneer, he created his own unique sound and his guitar skills surpassed the amount of credit that many today give to him.