WARNING: The following contains spoilers for Justice League: Endless Winter Special #1, by Andy Lanning, Ron Marz, Howard Porter, Hi-Fi, and Andworld Design, on sale now.
In Justice League: Endless Winter Special #1, the DC Universe's finest heroes fight an enemy from the past. An ancient monster known as the Frost King has been awakened, and he has just been made even more powerful thanks to Superman's Kryptonian crystals. Now, the Frost King has unleashed a new winter age on the world, plunging the entire planet under a blanket of snow, ice, and plummeting temperatures. And, to make matters worse, he has a legion of ice monsters that emerge from the storm, ready to attack any humans they come across.
The situation is more than dire and the biggest surprise is that this has happened to Earth before. Indeed, a long time ago, the Frost King attacked, and this leads to the formation of DC's first team of superheroes: Justice League Viking.
At the end of the Justice League Endless Winter Special #1, as the world becomes covered in snow, Black Adam can be seen observing the cold descending upon Kahndaq from his castle. "After all this time... how can it be happening again," he wonders. This is the first hint that the Frost King has attacked before and, immediately after that, everything flashes back to the 10th century, showing the start of Black Adam's involvement with this ancient threat.
In Egypt, the wizard Shazam is addressing a trio of characters, and he explains that while he has no wish to free Black Adam from his prison, he has no choice given the severity of the coming danger. A very long time ago, Teth-Adam was the wizard's first champion but, after he grew into a villainous force, the wizard trapped him in a tomb. While it was our understanding that Black Adam would only be awakened again in the modern era to face Billy Batson and the Shazam Family, it's now been revealed that Black Adam was actually awakened in the 10th century to fight the Frost King.
The wizard liberates his former champion, leaving Teth-Adam to meet three other super-powered beings: the elemental entity Swamp Thing, the Amazon warrior (and Wonder Woman's future mother) Hippolyta, and the obscure DC hero, Viking Prince. Together, they form a powerful trio, and yet they require Black Adam's help to save the world. Essentially, this is the very first iteration of the Justice League, centuries before Batman, Superman, and Wonder Woman would headline their own team.
This Viking team, which is comprised of old heroes and ancient, immortal entities appears to be DC's answer to Marvel's prehistoric Avengers. As part of the "Marvel Legacy" relaunch in 2017, it was revealed that the first iteration of Earth's Mightiest Heroes united in the year 1,000,000 BC to save the world from a dangerous Celestial. These original Avengers included Odin, Agamotto, the Phoenix, the first Black Panther, the first Iron Fist, and the original Ghost Rider, as well as the Starbrand.
Since the Frost King never took over the planet in the 10th century, the Justice League Viking will obviously be successful in saving the world, but somehow, Black Adam will also end up back in his tomb. But will it be of his own volition, or will the first Justice League turn on one of their own? Whatever the answer is, since Black Adam is the one of only very few who know about this ancient threat, perhaps he will see it fit to put his old team back together in the present. After all, they may be the only ones who can defeat the Frost King.