For the record, "titles" like this are kind of meaningless. So no, I dont think John Lennon should be called the "king" of rock, any more than any other of the Beatles should be. The Beatles were who they were because of what all them contributed. Now, to respond to a couple of posters here:
Chuck Berry was a good rock and roll/rockabilly guitarist. He certainly was nowhere near the top of the class though. He was influential, but there were others in that era who were much better and much more influential.
Elvis was Elvis. The main thing Elvis had going for him was his management, and the fact that many of the great black artists of the time could not get the airplay on many radio stations.
Guys who were better, more influential and maybe not remembered as they should be:
Carl Perkins. Elvis idolized HIM. He wrote "Blue Suede Shoes" and is referred to as the King of Rockabilly. Since that was what all these guys were playing, I think Carl deserves some consideration. The Beatles, Stones and many others consider him a major influence.
Eddie Cochrane: Wrote "Summertime Blues" and is recognized by the Beatles and many others as a great influence on their early music.
Little Richard: The consummate early rock and roller. The Beatles covered many of his songs. "Long Tall Sally" for one. Chuck Berry was good. Little Richard was unbelievable.
Smokey Robinson: THE songwriter that pretty much spearheaded Motown. His group, The Miracles helped transition rockabilly into Motown soul. He's been writing songs for six decades. And most of them have been classics.
Buddy Holly: This guy is remembered in song, but his contribution to music can not be measured. He was the first to write, perform and record his own music. He pioneered multitrack recording and other technical advances. The songs he wrote launced many careers. "Not Fade Away" by the Stones. "When Will I Be Loved" by many artists. The list goes on. If you want to call somebody a king, he might qualify.
I'm not saying that I have the answer. Heck, there are so many possibilities. I just think some of the people who never get the credit should be recognized.