Marvel has a knack for providing their devoted fans with glimpses of major characters and plot directions in post-credit scenes of their movies that seem to simultaneously confuse all those that aren't familiar with the comics (i.e. Thanos). The most recent scene occurs after Thor: The Dark World, with Lady Sif and Volstagg handing over the Aether to some white-haired dude with a lot of alien-stuff on display. As most of you know, the Aether is the Power Gem, so why would Asgardian warriors hand over something that important over to this creepy-looking dude, and why is he searching for the other five? Well, I'll tell you...
The Collector, also known as Taneleer Tivan, is an Elder. Elders are some of the oldest beings in the universe, hence their name. A defining characteristic among Elders is their lack of ageing and their resistance to disease. Most Elders use their long lifespan to increase their mind-power or strength of body. The Collector instead dedicated his life to acquiring objects to increase his power.
Taneleer Tivan spent the beginning of his life with his wife and daughter, but shortly after his daughter came of age and moved away, his wife lost the will to live, and simply ceased. Tivan was distraught with his wife's passing, and he searched for a new way to give his life meaning.
He had a vision that powerful beings were going to ravage the universe and bring an abundance of death, so he planned to acquire powerful objects before the forces of evil could. He built himself a spaceship, and traveled to every planet he came across to gain their finest possessions. He quickly filled his ship, so he stored all of his treasures in uninhabited planets. He ended up filling ten planets, calling them his museums.
Thanos (big purple-faced guy, you've probably heard of him) approached Tivan, interested in one of his artifacts: the Reality Gem. Thanos offered him a trade, the gem for The Runner, one of the last of the Elders who Thanos converted to an infant using the Time Gem. The Collector instantly agreed, seeing no value in the gem. His mistake.
So as you see, The Collector had no idea as to the importance of the gems, so why is he trying to collect the other five in the post-credits scene? We already know that Marvel doesn't always follow the comics, but seeing how The Collector is showing up in Guardians of the Galaxy, it looks like his collecting habits are more devious in nature. So what is his bargain? If he is working for Thanos, what does he expect to get in return?
Thanos could be holding The Runner hostage, or even Tivan's daughter. It also appears as if The Collector is holding Adam Warlock's cocoon in one of his cases, so perhaps he is holding him for Thanos as well. I'm pretty sure Tivan wouldn't do all this work for Thanos while expecting nothing in return, so ransom seems the best bet.
If you have any ideas as to The Collector's motives, feel free to voice your opinions below in the comment section.
If you could have an Infinity Gem, which one would you want?