On Wednesday night, Marvel, prompted by a leak, released the trailer to Avengers: Age of Ultron sending many comic book fans into a frenzied euphoria.

But to someone who doesn't have their nose buried in a comic book, it might be a little hard to understand what, exactly, is going on in this trailer and why comics fans are freaking out so much over, among other things, something called "Hulkbuster armor." Here, then, is a brief guide to what comic book fans are so excited about in the Avengers: Age of Ultron trailer.

Who is Ultron? Why is everyone so jazzed about Ultron?

Ultron, in the comics, is a robot sporting an advanced, evolving AI, who eventually becomes one of the Avengers' most vicious, cruel and powerful foes. He is a nerd's worst fears about the singularity come to life, or at least to ink. In the comic book series Age of Ultron, written by creator Brian Michael Bendis, he's taken over the world, turned it into a dystopian wasteland, and made superheroes inconsequential:

The movie is tweaking his origin story a bit by making him the creation of Tony Stark — a concern for comics purists. But what comics fans were really concerned about was translating Ultron's aesthetic (via believable CGI) and "big bad" quality from the comics onto the big screen. This scene of Ultron crushing what appears to be the skull of a War Machine/Iron Man-esque prototype is particularly poignant, because it's the first time we see that something may be very wrong with Stark's creation:

There's also a brief shot of a robot army …

... which calls back to the Age of Ultron comic book storyline:

And there's this final shot of the trailer, a close-up of Ultron's face, which seals the deal that Ultron will be true enough to his comic book presence. It's also proof that robots with eyebrows are scary:

Who is The Hulk fighting? Is that an Iron Man suit?

The biggest sustained fight scene in the trailer is between Hulk and what appears to be a bulky Iron Man suit:

And there are some take-your-breath-away moments, like Hulk throwing a car, then hurtling in like an NFL running back:

In the comics that's known as Hulkbuster armor — a creation of Tony Stark's that allows him to physically go toe-to-toe with The Hulk, one of the strongest characters in the Marvel Universe:

The armor does a couple of things. From a visual standpoint — in both the comics and the movies — it really emphasizes how big the Hulk is compared to the rest of the characters, adding a sense of scale. It also allows Hulk to beat up someone his own size.

From a story standpoint, the giant Iron Man suit really drives home how dangerous Hulk can be and what destruction he's capable of producing. According to rumors, the Hulkbuster armor is unveiled not because of Ultron, but because the Hulk has gone on a rampage and needs to be controlled. The Hulkbuster armor also shows a side of Iron Man that's important in comic books: he has often planned for his teammates to go awry, and has created countermeasures to stop them.

Like Ultron, there was a concern of how this would all translate onto the big screen. And the faint whimper you hear in the distance is the sounds of millions of fanboys and fangirls crying tears of joy that they maybe have gotten this right.

Who are the people I don't recognize?

There are two major characters and possible future Avengers in this movie. There's Quicksilver (Aaron Taylor Johnson), a supervillain-turned-superhero in the comic books who has the power of super speed. The second character is the Scarlet Witch (Elizabeth Olsen), who has the power to manipulate reality, probability, and tap into a thing called chaos magic in the comics. The two appeared in a post-credits scene in Captain America: Winter Soldier:

There are a couple of reasons why they're important. Both are major characters in the comics. Scarlet Witch is responsible for an event known as Decimation, which strips almost all mutants of their powers. But in the cinematic universe they're interesting in that they are the first Marvel characters that are both mutants and Avengers.

Fox, because of licensing deals hammered out during Marvel's touch with bankruptcy, has control over the X-Men, mutants, and X-Men villains. Marvel has control over the Avengers and every character that isn't associated with Spider-Man or the X-Men. Quicksilver and Scarlet Witch fall into the two company's rights and can be used by both companies — X-Men: Days of Future Past used Quicksilver this summer— but under certain restrictions (e.g. the two are both Magneto's children in the comics, but there will be a 0 percent chance this is will be mentioned in Avengers: Age of Ultron).

That said, people want to see their powers on screen for different reasons. In Quicksilver's case, fans will want to see whether or not his powers will be as stunning as Bryan Singer imagined them in X-Men: Days of Future Past:

From the trailer, we see brief glimpses of Quicksilver's super speed which is being treated with a glowing blur effect:

With the Scarlet Witch, Marvel has its first female character with superpowers. But we don't really know what those powers will be. Tapping into chaos magic and reality manipulation might be a little too complex for audiences first meeting the character. Whedon has hinted that he might ground her powers a bit more, saying in the past that Scarlet Witch "can weave spells and a little telekinesis [moving objects with thought], get inside your head."

The trailer doesn't answer this mystery.

Why does Captain America's broken shield matter?

The simple answer: the shield isn't meant to break. In the comic books, it's made from an indestructible (or something close to it) metal called vibranium, or an alloy of metals including vibranium. In the first Avengers film, the shield withstands an attack from Thor and his mythical hammer Mjolnir:

So if Captain America's shield is supposed to be indestructible and it's broken in the trailer, the unavoidable question is: what kind of power does Ultron have that he can break Cap's shield? And further, what does this mean for the Avengers and Cap if one of the strongest defensive items in their arsenal is broken?

It's a short shot, but it goes a long way in Ultron mythbuilding. Captain America's broken shield is also sending fans wild because of Marvel's upcoming plans to fully dive into a Civil War storyline in Captain America 3, a storyline that ends with the death of a prominent character and a rift between Avengers.

Why does Mark Ruffalo look like he needs a hug?

That's his thing. Ruffalo, who plays Bruce Banner a.k.a. The Hulk, is a character who has to keep his emotions in check, or else he turns into The Hulk and becomes a danger to everyone around him. Therefore, there are a lot of scenes where Banner's emotional state becomes the focus. That scene could also point to a defeat at the hands of Ultron or the aftermath of having to be restrained by Iron Man's Hulkbuster armor.

Recently, Ruffalo has said that he has a bigger and more complex role in the second film, and there have been further rumors that he and Black Widow (Scarlett Johansson) might be romantically involved. The trailer features what appears to be a scene where Hulk and Black Widow are holding hands:

What is the significance of Pinocchio's "I've Got No Strings" being used as the music?

It all goes back to the idea of Ultron. He started off as a creation like the puppet Pinocchio, and is given a new life and free will. And just like Pinocchio, Ultron has visions of wiping out humanity and creating a robot society to rule this world. (What? You didn't see the scene after Pinocchio's credits?)

This haunting tune gets at the idea of man not being able to control his creations. It just so happens that this theme is being explored in the current comic book arc called Axis.

But like, Captain America's shield, there's also a sense of continuity here too. Throughout the past few Marvel movies (Captain America: Winter Soldier in particular), there's been an implicit critique of government leaders and how they want to control the Avengers. And at the end of Winter Soldier, S.H.I.E.L.D., the agency that oversees the Avengers, is found to be rife with Hydra (a villainous terrorist organization) double agents. Without S.H.I.E.L.D. and without the faith of government leaders, the Avengers are going to be facing Ultron, for better or worse, with a newfound freedom — they've been cut from their strings, too.

A third reading on this is more serendipitous. In the last couple of weeks, we found out that Marvel will go ahead with and bring its Civil War storyline to the big screen. And Civil War's main theme is this idea of freedom and whether superheroes should be monitored by the government. The strings could very well apply to the other Avengers, who feel like Iron Man might be stringing them along.

Why are there ballerinas?

I have no good answer for this. This is wild speculation, but maybe they're part of a Black Widow flashback?

Last question: why is everyone so enthused about this trailer?

The easy answer is that a lot of people like The Avengers and a lot of people saw the first film. The Avengers ended up making over $1.5 billion worldwide, making it one of the most successful movies ever made.

The other answer is that the movie industry is now an industry that loves its trailers. We live in a world where there are teasers, teaser trailers, trailers, teasers to trailers (see: Mockingjay). The trailer for Avengers: Age of Ultron even had a release date before Wednesday's leak, and getting it a week early, even though we are months away from the movie's release, can feel like we're getting a treat ... even though it's just a trailer.

Avengers: Age of Ultron will be released on May 1, 2015