With the release of Justice League, DC has firmly established a cinematic superhero universe, with the addition of Flash, Aquaman and Cyborg to its established trinity of superheroes, Superman, Batman and Wonder Woman. In establishing a new cinematic universe, the film also makes a point to go into the history of this universe, and peppers into it a number of references to DC Comics book characters and possible future plot lines for other DC superhero films.

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Some of these Easter Eggs you will definitely have caught, while others may have slipped past even the most watchful gaze of hardcore fans. Here, we have collected the 15 of the most interesting Easter Eggs in the film, little references that either pay homage to the past, lay groundwork for the future or are just cute little jokes based on the history of the DC Universe. They aren't all game-changers, but they are definitely enough to crank the engine of both diehard fans and casual moviegoers, alike.

SPOILER WARNING: The following article contains major spoilers for Justice League, in theaters now.

15 THE GODS SHOW UP FOR THE PARTY

In a spectacular sequence in the film, Wonder Woman reveals the history of Steppenwolf's previous attempt to conquer Earth, which took place over a thousand years ago and was thwarted by a union between mankind, the Amazons, the Atlanteans and even a Green Lantern (the Green Lantern was so obscured that it is hard to even tell which alien race it was a member of)!

The fight was so massive that even the gods got involved. This was before the war of the gods as shown in Wonder Woman, so Zeus fought alongside Ares, with David Thewlis reprising his Ares role from Wonder Woman in a "blink and you'll miss it" cameo during the battle scenes. Robin Wright has a similar "blink and you'll miss it" appearance during the big fight as the Amazon general Antiope.

14 THE MOTHER BOX OF THE ROUND TABLE

After the decisive victory, the heroes of Earth had to decide what to do with the three Mother Boxes that Steppenwolf planned to use to create "Unity." They could not be allowed to be near each other, but even a single one of them contained massive amounts of power. So the Amazons, Atlanteans and the peoples of man decided to each take one of the boxes for safe-keeping.

The Amazons and Atlanteans could be trusted to simply guard theirs, but the people of Mankind were divided enough that they felt it had to be hidden so that no one would try to use it for selfish purposes. In a quick glimpse in the film, it appears as though King Arthur and Sir Bors were responsible for hiding the Mother Box at one point. Arthur and Bors have played major roles in a number of DC Comics, including Demon Knights and Shining Knight.

13 WHERE DID THE MOTHER BOX COME FROM?

This Easter Egg is a bit different, as it is so hidden that pretty much no one has ever seen it. As noted in the film, the Mother Box assigned to man was hidden over a thousand years ago. So how did it show up at S.T.A.R. Labs where Silas Stone could use it on his son, Victor? The Justice League film just notes that it was brought to the United States after World War I.

That seemed to be a pretty big detail to just handle in one line of exposition and sure enough, there was originally an epilogue of Wonder Woman where Etta Candy organized Steve Trevor's "Wonder Men" team to take the Mother Box to the States. It was deleted from the Wonder Woman film, but will be available as a bonus scene on the Blu-Ray!

12 THEY WERE STARMEN

In one of the oddest gags in the film, there is a quick bit where we see the front page of the Metropolis Post (presumably a less reputable newspaper than the Daily Planet). The front page is about the death of Superman. However, it bizarrely ties in Superman's death with two other notable celebrities who passed away in 2016, David Bowie and Prince.

Since Bowie and Prince were both rather eccentric performers, the conceit of this gag is that, to the people of the DC Cinematic Universe, their deaths would be seen in the same fashion as Superman's death. That seems to be a bit of a stretch (and borders on being disrespectful to the deaths of Prince and Bowie), but hey, it's the gag that they went with.

11 IT'S TUESDAY, THERE MUST BE A CRISIS

The aforementioned front page of the newspaper also had another headline that is very much a DC Universe Easter Egg. It notes that there is a "Citywide Crisis." That's no accident, as the word "Crisis" has taken on a very special meaning within the DC Universe. It all started back in the 1960s, when the Justice League of America and the Justice Society of America teamed up for the first time in "Crisis on Earth One" and "Crisis on Earth Two" in Justice League of America #21-22.

After a few other notable crises, the most famous one happened in 1985-86, where the Crisis on Infinite Earths changed the DC Universe forever, temporarily merging all DC Earths into one, single Earth. Infinite Crisis and Final Crisis have reversed those changes for the most part.

10 THE SKY IS RED -- THAT'S NOT GOOD

Once Steppenwolf successfully collected all three Mother Boxes and began the process of Unity, the Earth was in dire straits. The Justice League had to show up and break the Mother Boxes apart. During this epic battle, you might have noticed that the skies behind the League throughout the battle were red. That was no accident.

You see, as a really cool piece of foreshadowing, all DC Comics titles in the months leading up to Crisis on Infinite Earths began to have red skies in them. No explanation, just suddenly everyone had red skies showing up, leaving the characters mystified. It was all explained once Crisis officially began, but it was nice to see them pay homage to the red sky history in Justice League.

9 GOING BACK TO THE START

Something that Zack Snyder is famous for in his comic book films so far is an express desire to pay tribute to the comic book artwork that inspired the film. His first two comic book films, 300 and Watchmen, were stunning in how much of the original visuals that Snyder adapted into the film. 300 was just shy of seeing the actual comic book animated like those old 1960s Marvel cartoons where Jack Kirby and Steve Ditko artwork was just manipulated by animation.

In Batman v Superman: Dawn of Justice, Snyder recreated the famous first issue cover of the Dark Knight Returns. In Justice League, Snyder went back to Batman's first appearance on the cover to Detective Comics #27 in this shot from the final battle against Steppenwolf and the Parademons.

8 A HINT FOR BLACK MASK?

In the opening of the movie, Batman stalks a burglar in Gotham City. As it turns out, Batman is simply torturing the criminal so that he becomes terrified of Batman. Batman does this because he knows that Parademons are drawn to fear, so he is using the burglar as bait. During that scene, we see some Gotham City signs. One of them is for Janus Cosmetics.

Janus Cosmetics is the company owned by the parents of the villain who would eventually become Black Mask (yes, there is a Batman villain whose origin is directly connected to a company named after Janus, the Roman god who literally has two faces, and yet is not actually Two-Face). Since Black Mask is rumored to be the villain in the upcoming Gotham City Sirens film, that is likely no coincidence that it got name-dropped.

7 A SPECTRE OF THINGS TO COME?

Despite not having a whole lot of screen time, JK Simmons does an excellent job as Commissioner Gordon. In one of those few scenes, he is questioned by one of his men over the fact that people keep seeing scientists kidnapped by Parademons, but since no one has a photo of them, the descriptions of the Parademons sure sound like Batman. So, does Gordon believe that maybe Batman has snapped?

The answer is no, of course, but the Gotham City detective asking Gordon about the possibility is none other than Crispus Allen, who was introduced during Greg Rucka and Shawn Martinbrough's Detective Comics run. Allen later became the new Spectre during Infinite Crisis. It is unlikely that this is anything more than a cameo, but who knows?

6 BLAST FROM THE PAST

In choosing to cast Ben Affleck as Batman in Batman v Superman: Dawn of Justice, Zack Snyder specifically was looking to use a Batman who had been around the block a number of times. This was because he wanted the film to be highly influenced by Frank Miller and Klaus Janson's Dark Knight Returns, in which Batman has returned to crimefighting after a decade-long retirement.

In that first film, there were not too many references to Batman's long past as a hero, but in Justice League, there are some more discussions between Batman and Alfred over the fact that Batman has been doing this for so many years. One of the references was to fighting exploding, wind-up penguins. You know, just like what Batman actually did in 1992's Batman Returns, when facing off against the Penguin.

5 THIS JIMMY OLSEN MAKES IT OUT OF THE MOVIE ALIVE

In a nice tribute to the films of the past, Marc McClure, who played Jimmy Olsen in the Christopher Reeve Superman movies (he also played Marty McFly's older brother in Back to the Future), appeared in this movie as the guard at the prison that Barry Allen has to check in with before entering to see Henry Allen. McClure gets a funny line where he jokes with the guest who follows Barry (after the guest accosted Barry, Barry then drew glasses and a mustache with a marker at super speed).

After Batman v Superman: Dawn of Justice seemingly killed off Jimmy Olsen as an Easter Egg, this was a nicer Jimmy Olsen-related Easter Egg by Zack Snyder. It follows in the footsteps of the Reeve Superman films paying tribute to the actors from the Superman serials and the Superman TV series.

4 WUBBA LUBBA DUB DUB!

When Bruce Wayne sneaks into Barry Allen's makeshift secret headquarters, he keeps the lights off, waiting for Barry to enter and turn everything on. When Barry does so, not only does he have a bunch of computers running, but he also has a few different television sets going, likely speaking to how much stimulation Barry needs at all times due to his super speed.

One of the TVs is playing an episode of Rick and Morty, "Something Ricked This Way Comes," where Summer goes to work for a man who sells cursed merchandise. In the end, Summer and Rick get revenge on him by simply bulking up and beating him up. You could argue whether that is almost a commentary on the very idea of superhero vigilantism.

3 MAZEL TOV ON THE FILM, BARRY!

One of the jokes about Barry Allen over the years has always been that he was a bit lacking in terms of personality. He was just that really great, heroic guy that you don't really know anything about other than the fact that he's a good guy. This is highlighted by the fact that DC revealed that Barry was Jewish in a comic book in the late 1980s.

The story was set in the past, since Barry was dead by then, and it somehow has not been mentioned again. That is, until the Justice League film, of course, as Barry Allen subtly drops in that he is "a good Jewish boy." It might have been intended as a joke, but it actually does tie in with the history of the character.

2 ONE NATION UNDER GRODD

Also within the film, Barry nervously pointed out other characteristics about himself, including the fact that he speaks sign language. He then followed that up by quickly noting that he meant specifically gorilla sign language. This, of course, is almost certainly a reference to one of the Flash's greatest foes (and the Flash has one of the best Rogues Galleries in all of comic book history).

Gorilla Grodd is a telepathic and telekinetic gorilla from the mysterious place known as Gorilla City, which is filled with super-intelligent gorillas (aliens visited years ago and evolved them into a super race). Since we saw that the film established that obviously aliens have shown up on Earth in the past, it would be very easy to establish Gorilla City in the DC Cinematic Universe, as well.

1 TRUTH AND JUSTICE...PERIOD

There is a pointed moment during the final battle with Steppeneolf where Superman notes that he is a proponent of truth and justice. This, naturally, is a reference to Superman's famous catch phrase which notes that he stands for "Truth, Justice and the American Way." However, the film omits the "American Way" part and that will likely rankle some people.

The film's version, though, is actually what Superman's original catch phrase was on the Superman radio series, where he fights "a never-ending battle for truth and justice." That's what was in the Fleischer cartoons, as well. It wasn't until 1942, when America was at war, that "the American Way" part was added. After the war, though, it was dropped! It was in the rampant Anti-Communism era of the 1950s, where people had to prove that they were "for America" that the "American Way" part was added for good.

Did you see Justice League? What did you think?