"One down, five to go.." with those few words the Marvel cinematic universe set in motion events that will lead to a motion picture adaptation of the legendary Infinity Gauntlet storyline. The appearance of the mad Titan Thanos during the post credits stinger of The Avengers (2012) introduced the character and The Collector's words in the post credits stinger for Thor: The Dark World ignited the race to claim the Infinity Stones which power the gauntlet.
During phase one of the MCU the audience was introduced to the Infinity Stone called The Tesseract. Hunted by The Red Skull in Captain America: The First Avenger the Tesseract was tapped for its energies to create the weapons of HYDRA and when barehandedly wielded by the Skull during the climatic battle with Captain America seemingly transported him off world. The fate of the Tesseract was revealed when Howard Stark recovered it from the ocean depths. In The Avengers Loki was tasked with securing the Tesseract from earth by The Other who unknown to the audience at the time was working for Thanos. Loki's defeat saw Thor return to Asgard with The Tesseract and Loki. It is unknown to moviegoers what SHIELD was able to do with The Tesseract during the 70 years or so it was in their possession.
In Thor: The Dark World 2013 we are made aware of the existence of another Infinity Stone, The Aether. After securing it from the Dark Elves we last saw it in the above scene being entrusted to the care of The Collector. As was stated it is not a good idea to have two stones in the same place at one time.
The Power Stone
Last month saw the release of [Guardians of the Galaxy](movie:424073) and with it came another Infinity Stone, the Orb. The Orb is actually the housing for the stone itself. Marvel has designated this stone as the Power Stone. In Marvel Comics the stones are referred to as gems with distinct names. Power, Mind, Time, Soul, Space and Reality. If the Tesseract can be considered the Space stone then The Aether can be considered the Reality stone perhaps. During "Guardians" The Collector explained the origins of the stones and accepted the Orb from Peter Quill/StarLord without revealing his possession of The Aether. The film ended with the Orb being in the care of the Nova Corps but no mention of the fate of the Aether.
Some have speculated that Loki's staff in The Avengers was the Mind Stone. In "The Art of Guardians of the Galaxy" book there is a three page foldout highlighting the three previously mentioned stones detailing their appearances. No mention is made of the staff or its existence. One would have to question the reasoning behind Thanos, who is trying to amass the stones giving one away to Loki. Also if it were an Infinity Stone I am sure Thor would have recognized it and also took to Asgard with the Tesseract.
So here we are approaching the conclusion of phase two and we are only halfway through our introduction to the various stones. Probably as Thanos' presence is revealed to The Avengers a race to collect the outstanding ones will ensue. Most are speculating this epic showdown to take place in [The Avengers 3](movie:738027) giving us an unknown amount of films to set things in motion. The gauntlet itself (which one must wear to contain the stones) was glimpsed in Thor 2011 secure in Odin's vault.
With Loki's sitting clandestinely on the throne in Asgard revealed in the end of [Thor: The Dark World](movie:206462) he now has access to the Tesseract and the ability to pay his debt to Thanos, whom he was warned "there is no place you can hide from." All of this sets up the possibility of a Thanos, Red Skull and Loki super-villain team-up vs. The Avengers and possibly Guardians of the Galaxy!