The formation of the titular team may have been the focus of Justice League, but a lot of people seem to agree that one of the best sequences had nothing to do with Superman, Batman, or Wonder Woman. The movie features a flashback to thousands of years ago when the armies of man, Atlantis, and the Amazons combined forces to repel Steppenwolf (Ciaran Hinds) from conquering the Earth using his Mother Boxes. Though it's a short sequence, the battle is filled with enough action and cameos to make any comic book fans smile. It runs the risk of sensory overload during the first viewing, so there's a chance not everyone managed to catch all the different characters who show up.
In addition to the Amazons and Atlanteans, the Old Gods (first shown in Wonder Woman) and even a Green Lantern can be seen battling back Steppenwolf and his parademon army. None of these characters are named onscreen, but thanks to internet theorists, IMDB, The Justice League: Art of the Film book, and our own nerdy brains, we were able to place the biggest characters from the epic flashback. Without further ado, these are all the major DC characters to be found in the flashback
Hippolyta
Created by Zeus, the Amazons are basically ageless, which means that several of the characters first introduced in Wonder Woman can play a big part in the backstory of the DCEU. The most notable of the Amazons is their queen and Wonder Woman's mother, Hippolyta. Connie Nielsen reprises her role and while she can be seen much more prominently in an earlier scene on Themyscira, she does appear in the flashback leading her people against Steppenwolf. The Amazons were trusted to protect one of the three Mother Boxes for safekeeping, which they ultimately fail to do.
Zeus
Wonder Woman's mom wasn't the only parent she had out on that battlefield. Zeus, king of the gods and Diana's secret daddy, can be seen a few times during the flashback scene. Looking like more of a Classic Hero with his short cut beard and robes, he's one of the three giant human-like beings that tower over the rest of Earth's forces. Zeus hurls thunderbolts at Steppenwolf, which led some to believe that he may have been some ancient form of Shazam. Thanks to IMDB credits and alternative concept art, we can confirm that this was Zeus. It's likely soon after this battle that he meets his ultimate fate against Ares. Speaking of which...
Ares
Ares is one of the three Old Gods that lend a hand in combating Steppenwolf. While Ares doesn't get as much screen time as Zeus, his distinctive helmet can be briefly seen on the battlefield. He leaps at Steppenwolf while the invader is blasted by lightning from Zeus. Being the God of War, Ares wouldn't have missed his chance to partake in one of the most important battles in history. Eventually, Ares would slaughter all of the Old Gods, before he finally meets his end at the hands of Wonder Woman centuries later at the end of World War I.
Artemis
The final of the Old Gods to participate in the battle is Artemis, as is revealed thanks to the credits. She didn't look anything like the above photo (that's how she appeared in the New 52 relaunch) but instead, she was a more humanoid woman in leather armor in the movie. Artemis is the Goddess of the Hunt, and is known for her skills with a bow and arrow. She's the giant lady who shoots down an entire spaceship with a golden arrow, showing an impressive display of power alongside her fellow gods. Artemis eventually dies at the hands of Ares.
Atlan
Ancient Atlanteans, the ancestors of Aquaman, also had a major part to play in the battle against Steppenwolf. The only prominent figure among them is an unnamed Ancient Atlantean King played by Julian Lewis Jones, as seen in the above behind-the-scenes photo. (He's the one holding a trident). While his character goes unnamed in the movie, comic books fans will likely guess that this is Atlan, the first king of Atlantis. In the comics, he's betrayed by his brother and swore a grudge against Atlantis, sinking it to the bottom of the sea. He rises from the dead centuries later as an Aquaman villain, which would certainly be an interesting story for live-action. Is it so far-fetched to think that the DCEU is already setting up for this storyline?
Mysterious Green Lantern
Fans theorized for years that Green Lantern would be cameoing in Justice League, and while it wasn't what they were expecting, a Green Lantern certainly showed up. A Green Lantern of an unknown alien species can be clearly seen as a part of the flashback battle fighting alongside the good guys. The alien is killed by Steppenwolf and his power ring is shown flying off into space to find a new user. The mysterious Green Lantern has no name, but Reddit user StrandingDeath posted a theory that the character is Yalan Gut, a SUPER obscure Lantern from the comics. StrandingDeath points to the characters clothes, ears, and unique snout as the evidence behind his theory. It's unconfirmed, but it's as good a guess as there is right now.
Desaad-Like Priests
No other New Gods are in Justice League other than Steppenwolf, but the flashback does showcase some unique characters that may have flown under the radar. When Steppenwolf tries to unite his three Mother Boxes to form The Unity, a group of robed priest-like figures is seen with the Boxes. Based on how they are dressed, they share quite a similarity to Desaad, a New God on Apokolips who serves Darkseid. What skills Desaad lacks on the battlefield, he makes up for in torturing, but the DCEU could be reworking him to be some kind of head of an Apokoliptan religion.
