I was watching a discussion about the movie earlier today, and one of the main points the filmmaker wants to make is Elvis was not the King of Rock & Roll, Little Richard was. It's sad that all these years later, people are still accusing Elvis of being a racist who just stole music from black people. Elvis never asked people to call him "the king". Even Richard seemed to have backed off of that in later years. I saw one talk show where he said 'Elvis and I are friends, and we know who the King is, he's up above us, but I am the originator, the emancipator, the architect of rock and roll".
I love both, but I would definitely consider Richard and maybe Chuck Berry as the 'true' Kings of Rock n' Rolll. Elvis was a far more versatile artist.