WHEN ELVIS PRESLEY STROLLED onto the stage for his last performance, there was something different about him. His face had swelled, and his gut was pregnant with obesity. His hair and signature sideburns overran his head and face, and his movements, karate kicks, and hip swivels, were no longer crisp or energetic. He could still sing--he never lost that--and he still had a charismatic stage presence, and he could still send fans into a frenzy. But for years leading up to his death, it seemed the brightness that once shone from this superstar came more from his sequin-adorned jumpsuits than...