WARNING: This article contains SPOILERS for Justice League
The Justice League movie did more than unite the superhero team - it may have revealed Zeus and the Greek Gods walking the Earth. That's not as shocking a revelation for DC fans as it would have been before Wonder Woman created a new mythology for the version of Earth created in Zack Snyder's Man of Steel (the home of the DC shared movie universe). In that mythological history of mankind, the Olympian Gods - Zeus, Ares, Athena, Poseidon, and all the rest - once lived in harmony with humanity. Until the God of War did what he does best, and sowed evil and hate in Zeus's creation, dividing mankind for all time...
Of course, Justice League seems to have added another wrinkle to that story. Not necessarily a change, update, or retcon (although Justice League was changed a ton), since it's still Wonder Woman who shares this new history lesson of gods and men. When explaining the mission of Justice League's villain, Steppenwolf, and why his first attempt to crush Earth failed... Diana adds a new, heroic chapter to the history of DC's Earth.
One in which Atlantis, the Amazons, and humans were united. And when each race's greatest leaders knew Zeus and his superhuman children personally.
That's what audiences are led to believe, provided they soak up every detail of the ancient battle sequence revealed in the movie. The one in which an alien Green Lantern finally appears, and even a young Antiope slaughters Parademons millennia before Diana is even born. Before the movie was actually released, the images of what looked to be Zeus in Justice League's battle threw fans for a loop, since Wonder Woman had so recently revealed him as Diana's true father (a suspension of disbelief sizable enough for fans of simple, magical superheroes).
But as long a shot as it may have seemed, the evidence supported the most compelling theory: that Justice League would make good on the promises given to the reporters and bloggers who visited Snyder's set. The Justice League would begin a new "Age of Heroes," but audiences would get to see the original, pre-historic one too. One in which the gods who shaped the world before dying and passing into legend and myth saved Earth from invasion.
And in the actual movie, the identity of that lightning-thrower is effectively confirmed to be Zeus, Wonder Woman's father.
It isn't explicitly pointed out, since that wouldn't make much sense in the narrative frame of Diana telling the story. Some may take issue with the lightning-wielder's appearance: young, dark-haired, short-bearded, and otherwise un-Zeus-ish. But remember, this is far enough in the past that all record of it was lost to human records. And judging by Diana's absence, and the Amazons' more 'tribal' aesthetic, early even in their history. Zeus was still dark-haired in the history lesson of Wonder Woman, and wielding lightning in almost the exact same way - which means the figure seen above is most likely Zeus in the prime of his life and power.
Were he alone in his superhuman powers or stature in the scene, there may still be some doubt. But Diana does specify that "the gods themselves" joined in the fight, and Zeus isn't alone. Aside from the leaping warrior taking Steppenwolf on up close, there's also the glowing archer who fires an arrow that destroys an entire Apokoliptian ship - a figure identified in the credits as Artemis, the Goddess of the Hunt in Greek mythology (and known to the Romans as Diana). Strip away all the other facts, and Olympian gods battling Steppenwolf makes Zeus's presence almost mandatory. And he was there, hurling his thunderbolts, and towering over the warriors allied beside him.
Judging by the reports of just how much Joss Whedon changed of Justice League, it seems like this mythology was originally going to be more substantial. Not only in terms of the role Diana's divine, extended family played, but of the fate of Atlantis and the Amazons following the battle. The shorter theatrical cut is no more specific than it has to be, but for the Wonder Woman fans out there, take this ancient battle as one of many Zeus fought before his union with Queen Hippolyta. And just one more story Diana heard as a child, never knowing the gods were her brothers and sisters.
Here's hoping the full story is told in future DC movies, or it's revealed exactly how much Diana knows of her Olympian family's history.