Feige On Thanos Plans

Marvel's President Kevin Feige, tells MTV that the Thanos cameo at the end of The Avengers did exactly the job it was meant to do - "get the audience buzzing". 

“Clearly, there’s a purpose to us putting him in the end of that movie. We do have plans for him. I wouldn’t say we ever feel the need to rush anything one way or the other. We succeeded in Phase One because we stuck to our guns and stuck to the plan. That plan took place over many, many years and it ultimately paid off. I see Phase Two unfolding in the same way of us taking our time, us doing what’s right for each individual movie, while folding in elements that will not only build up to the culmination of Phase Two, but even Phase Three.”

Since Thanos will appear in the final two 'Phase Two' films - James Gunn's "Guardians Of The Galaxy" and "The Avengers 2" - this pretty much means that he is the primary villain in at least one (if not both) of these movies.