Avengers: Age of Ultron opened over the weekend, and based on its colossal box office numbers, there’s a pretty good chance you saw it. If you did see it, there’s a good chance you’re the kind of person (like me) who’s really into comic books and superheroes and all the minutiae that entails, and you know the Marvel Cinematic Universe by heart. But there’s an equally good chance that you’re not that kind of person, and you just went to the movie because you thought explosions and wisecracks and an army of robots would be cool.

If you’re the second kind of person, there’s an even better chance that the brief mid-credits scene at the end of Age of Ultron left you feeling at least a little head-scratchy, even if you have seen all the other Marvel movies. If that’s you, you’ve come to the right place, because I’m about to break the context of that moment down for you, and then you can go amuse your friends with your newfound knowledge of comic bookdom. It’s fun to be a nerd, kids!

Oh, and if you haven’t seen Age of Ultron at all yet, now might be the time to look away, because we are entering SPOILER TERRITORY.

So, first thing’s first: the big dude with the purple skin is Thanos, a superpowered cosmic being with a massive ego and an even more massive lust for power. If you recognize him, it’s because he first showed up in the mid-credits scene of the first Avengers movie, and then showed up again with a more substantial role (and a rocket throne, which I have to believe Kanye West is putting serious dollars into building for himself) in last year’s Guardians of the Galaxy. That glove he put on his hand is, for the moment, just a cool-looking glove, but Thanos has big plans for it. He wants to turn it into The Infinity Gauntlet.

You might’ve heard that name before, and you should probably get used to hearing it because it’s going to be one of the driving forces of the Marvel Cinematic Universe for at least the next four years or so. First introduced to Marvel Comics in 1990, the Infinity Gauntlet is a massively powerful glove that contains the six Infinity Gems, powerful cosmic objects that give their owner incredible abilities, and if someone happens to get all six, they’re basically unstoppable. It’s wearable God Mode, so you can see why Thanos would be into that.

The six Infinity Gems introduced along with the gauntlet are the Soul Gem, the Time Gem, the Space Gem, the Mind Gem, the Reality Gem, and the Power Gem. Each gem has powers that basically correspond with its name, so the Time Gem can grant you time travel, the Mind Gem mind control, and so on. In the Marvel Cinematic Universe, these are referred to as Infinity “Stones” rather than Gems, but they work the same way.

As Thor notes near the end of Age of Ultron, four of the six Infinity Stones are already floating around in the Marvel movies, though not all of them were called that when they first appeared. The Space Stone is the Tesseract, that thing Loki uses to open a portal to Earth in The Avengers. The Reality Stone is the Aether, the red stuff that almost unmakes existence in Thor: The Dark World and is later entrusted to The Collector (Benicio del Toro) in the film’s mid-credits scene. The Power Stone is the purple stone that served as the MacGuffin for much of the action in Guardians of the Galaxy, and also came with both the first in-movie explanation of what an Infinity Stone is and the first in-movie appearance of Thanos trying to gets his mitts on one. And then there’s the Mind Stone from Age of Ultron, which is what gave Loki’s staff the power to control people, and for the moment is safely tucked into the forehead of Vision (Paul Bettany). We don’t know where the other two are yet, but all in good time…

As you may recall from Guardians of the Galaxy, Thanos tasked Ronan the Accuser (Lee Pace) with getting the Power Stone for him, only to watch Ronan take the stone for himself. So, when Thanos says “I’ll do it myself” during Age of Ultron’s mid-credits scene, that’s the signal that his personal hunt for the Infinity Stones is about to get even more personal, so much so that it’ll wind up on the doorstep of The Avengers.

That’s the setup for Avengers: Infinity War, the two-part mega-movie arriving in 2018 and 2019 that will pit The Avengers (and likely the Guardians of the Galaxy) against Thanos for a massive cosmic battle over the Infinity Stones and the gauntlet that holds them. The stakes will be high, and though we don’t know just how high yet, we do know that Infinity War will be at least loosely based on The Infinity Gauntlet, a 1991 Marvel Comics miniseries in which Thanos — while wielding the Gauntlet — literally wipes out half of all sentient beings in the universe with a snap of his damn fingers.

So yeah, if you thought these Marvel movies were crazy now, just wait a while.