The deal was this: LIFE photographer Bill Ray would be the only photographer allowed in the Kansas City Chiefs’ locker room during the first Super Bowl, then known as the AFL-NFL World Championship Game. He would have unrestricted access to the action off the field that day, but LIFE could only publish the photos if the Chiefs won. They lost to Vince Lombardi’s Green Bay Packers, 35-10, and the photos never ran. Now, as the NFL Network prepares to air complete footage of that game for the first time since the original broadcast on Jan. 15, 1967, Ray tells the stories behind those rarely seen photos. “There was a big buildup to this championship,” he tells TIME. “There was real animosity between these two leagues. The National League, which was an old established league, did not see the advantage of this newer league being established. They didn’t understand that this would become a boon to both of them.” Though the teams looked more or less even on paper, Ray recalls, word got out that the Packers considered the Kansas City Chiefs to be a “Mickey Mouse” team. So the Chiefs got dozens of Mickey Mouse ears and wore them, Ray says, “in the locker room, before the game, half-time—I’m not so sure they were wearing them after, but that was kind of the idea, that the pictures would be funny if they turned out to be the champions.” Things were still looking fairly even at halftime, when Ray photographed Coach Hank Stram giving a pep talk to the team. “On the ground, the number of yards gained and everything was favorable to the Chiefs even though they were down a few points,” says Ray. “And then they got run over in the second half.” After the game, instead of donning their Mickey hats and rubbing the Packers’ insult back in their faces, the Chiefs found themselves in a somber mood. “If you lose, it’s a wake,” Ray says. “People aren’t talking, they’re just getting showered and getting the hell out of there.” Despite the Chiefs’ loss that day, the roster on both sides would turn out to be legendary: Both coaches and both quarterbacks, the Packers’ Bart Starr and the Chiefs’ Len Dawson, would later be inducted into the Hall of Fame. And the Super Bowl would balloon into the mega-event it’s become today, despite the fact that one-third of the stadium’s $12 seats remained empty during that first game. But the citizens of Los Angeles must have known that history was taking place that day. For two days before the game, Ray wandered around the city photographing desperate residents who, in light of the broadcast being blocked in the local TV market, were “getting up on their roofs, putting all these jerry-[rigged] antennae up to try to get it from Santa Barbara.” And Ray will never forget that day, either. The game was pretty eventful, but he has another reason to remember it: his wife went into labor and gave birth to their daughter later that night. Bill Ray—The LIFE Picture Collection/Getty Images For more of Bill Ray’s work, visit www.billray.com. Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter @lizabethronk.