Okay, if you haven't already figured it out by now, the MCU is currently revolving around Thanos and his quest to retrieve all six Infinity Stones for world domination. Typical bad guy. The thing is, they've been setting this up ever since Thor (2011), with the extremely brief cameo appearance of the Infinity Gauntlet.
Took me a while to find it for myself, but there it is. The weapon Thanos used to kill half the universe by snapping his fingers. After this appearance, it wouldn't take long for an Infinity Stone to finally appear. The first Infinity Stone we would see would come later that year in Captain America: The First Avenger with the appearance of the Tesseract, or the Space Gem.
The next Infinity Stone would appear in Thor: The Dark World with the appearance of what the Elves and the Asgardians called the Aether, but us comic fans know it better as the Reality Gem.
The most controversial stone yet would appear in the best Marvel movie of it's time, The Avengers. We actually saw two Infinity Stones here. The reappearance of the Tesseract (Space Gem) and the gem in Loki's Scepter.
Loki showed the true power of the two Infinity Stones by mind controlling everybody and opening a wormhole in space, thus beginning the Battle of New York, the war between The Avengers and The Chitauri. It was confirmed in the newest Marvel and Avengers sequel, The Avengers: Age of Ultron that the gem in Loki's Scepter is in fact the Mind Gem. And of course, like Marvel rarely does, they stuck to the comics and put the Mind Gem in the Vision's head.
It was made apparent that Vision is J.A.R.V.I.S in a artificially intelligent body designed by Ultron. But you could have found that out your self if you havent already. The next Infinity Stone we saw actually came several months prior to Avengers: Age of Ultron in the movie we all loved, Guardians of the Galaxy with the appearance of The Orb, or the Power Gem.
Boom. So in just four short years, Marvel has given us the Space Gem, Mind Gem, Reality Gem, and Power Gem. That leaves two Infinity Stones unaccounted for, the Time Gem and the Soul Gem. But when will we see such stones? I'm pretty sure all the Marvel fans with common sense know that the Soul Gem, just like Vision with the Mind Gem, is located at the base of Adam Warlock's forehead. We've already seen Adam Warlock in his cocoon stage (see [Thor: The Dark World](tag:206462) and GotG), but we have yet to see his full body appearance. My guess is that we will see the Soul Gem and Warlock in their entirety in Guardians of the Galaxy 2 coming in 2017.
However the appearance of the Time Gem still remains a mystery. My best guess is that we will either see the Time Gem either of these three upcoming movies: Black Panther, Doctor Strange, or Captain Marvel. But it all comes back to Thanos. Every movie that Marvel has made since 2011 is building up to what will be the biggest Marvel movie ever made: Avengers: Infinity War.
As you can see, the movie will be so big, so awesome, so badass, that 2 hours and 30 minutes just won't fit everything in. Yup, the third and biggest Avengers movie will be split into two parts. So everyone, mark your calendars and from now on whenever you watch a Marvel movie, keep your eyes peeled.