Once you've discovered the groundbreaking R&B that led to the explosion of rock n’ roll, a figure like Elvis Presley seems less like an innovator than a charismatic, reverent interpreter. (If you are less charitable, you could call him a ripoff artist.) He’s a hell of a singer, though, and practically every song he touched became the definitive version. In fact, each of these songs, from the guileless “Rock Around The Clock” to the one-good-joke “Tequila,” can still shake up a dance floor, possessed by the electricity of a whole musical universe cracking open.