When the credits rolled on The Avengers back in 2012, patient audiences were treated to a cameo appearance from one of the biggest bads in the entire Marvel universe: Thanos, the “mad titan” who was the puppet master behind the Chitauri invasion of Earth. Since then, Marvel’s mid-credits stingers have rapidly evolved in importance, teasing future movies and setting up characters who would become significant years down the line. Avengers: Age of Ultron is no different and the mid-credits scene on the sequel hints at even more massive events for Phase Three of the Marvel Cinematic Universe.

Major spoilers for Avengers: Age of Ultron follow. Tread cautiously.

During the course of their latest adventure, the Avengers learn what superhero-savvy audiences have already put together: the “MacGuffins” that have been driving the past couple of movies aren’t just regular old artifacts of immense power – they are the artifacts of immense power. The Tesseract (seen in The Avengers), the Aether (seen in Thor: The Dark World), the Orb (seen in Guardians of the Galaxy) and the gem on Loki’s staff (which plays a major role in Avengers: Age of Ultron) are actually Infinity Stones.

But what are Infinity Stones, you ask? They’re the most powerful objects in the entire universe, each of them tied to a specific aspect of existence. The Tesseract is actually the Space Stone, Loki’s scepter is powered by the Mind Stone, the Aether is the Reality Stone, and the Orb is the Power Stone. There are two other Infinity Stones, the Time Stone and the Soul Stone, that haven’t been seen. Yet.

Still with us? Okay. Good.

The mid-credits tease in Avengers: Age of Ultron finds Thanos, still voiced by Josh Brolin, finally up and out of that nifty hover throne we saw in The Avengers and Guardians of the Galaxy. Yes, after half a dozen movies, the most evil being in the universe has finally decided to stand up. More importantly, we see him opening some kind of safe and within that safe is a giant golden glove. A gauntlet, if you will. Thanos then speaks:

Fine. I’ll do it myself.

It’s about time! After five movies of him watching from the shadows as the Infinity Stones change hands, it looks like he’s finally going to start getting proactive.

So, what happens if Thanos gets his hands on the Infinity Stones? As any Marvel fan will tell you, Thanos’ most famous storyline involves him using all six of them to create the Infinity Gauntlet, which gives him total power over the entire universe. Naturally, each and every superhero from Earth and every other corner of the galaxy is called in to help take him down. Things get dramatic, heroes fall by the dozens, the entirety of existence is threatened and the result is one of the most famous stories in comic book history.

Yep, that certainly sounds like material worth adapting for the massive, Avengers: Infinity War, which will arrive in two parts in 2018 and 2019. And since Marvel’s Phase Two has been all about introducing us to the Infinity Stones, Phase Three will undoubtedly be all about Thanos slowly collecting those stones so he can assemble his ultimate weapon.

Will that means Thanos showing up in the already jam-packed Captain America: Civil War? Probably not. However, his presence will probably be required in Guardians of the Galaxy 2 (where two members of the team already have a bone to pick with him) and Thor: Ragnarok, which will see Asgard face the Norse apocalypse. We don’t know enough about the other Phase Three movies to speak definitively, but we do think that the mystic Doctor Strange sounds like an awfully good place to introduce the Soul Stone. Could Benedict Cumberbatch’s Sorcerer Supreme be the first Earth superhero to meet the universe’s ultimate enemy face-to-face? Maybe! Could he also rear his ugly purple head in Black Panther or Captain Marvel and could either of those films introduce the Time Stone? Once again: Maybe!

In any case, expect much of Phase Three to involve the Marvel Cinematic Universe falling apart so the arrival of Thanos will force everyone to team up for their biggest mission yet. Avengers: Age of Ultron has already set the stage. We’ve seen the fissures between Tony Stark and Steve Rogers that will lead to all-out conflict in Captain America: Civil War. Thor is heading home to face the literal end of his world in Thor: Ragnarok. While the heroes’ personal worlds crumble, Thanos will be gathering those stones ... and we know exactly where they are, so he probably does, too.

The Space Stone is locked away in Asgard. The Power Stone is in a Nova Corps vault. The Aether is in the possession of The Collector. The Mind Stone is planted in the middle of The Vision’s forehead. Expect anyone near these locations (or androids) to not have a very good time over the next few years. The MCU is going to get awfully rough for characters not named Thanos.

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