The 1960s may have been a wildly transformative decade in the history of popular music, but for Elvis Presley it was something of a black hole.

When he returned from his two-year hitch in the Army in 1960, the king of rock ’n’ roll essentially retired from live performing, confining himself to making movies (which were growing steadily worse) and recording disposable pop songs (that were no longer reaching the charts). A much-praised television comeback special on NBC in December 1968 had put him back on the radar. But when he finally returned to the stage for the first time in more than eight years, for a four-week engagement at Las Vegas’ new International Hotel, there was no guarantee he could still deliver onstage.

This week marks the 50th anniversary of Elvis’s Vegas comeback show, on July 31, 1969 — a milestone being celebrated by a new Sony 11-CD boxed set of his ’69 Vegas performances, a reunion concert in Memphis next month and probably some snickers from the rock classicists. Elvis’s Vegas years are mostly recalled as a period of commercial excess and artistic decline: the bombastic shows, the gaudy white jumpsuits, the ballooning weight, the erratic stage behavior, the drugs. “For many,” wrote Dylan Jones in “Elvis Has Left the Building,” “Vegas Elvis was already Dead Elvis.”

But for that 1969 comeback, and at least a year or two after, Elvis was at his peak as a stage performer, and he created a show that not only revitalized his career, but changed the face of Las Vegas entertainment.