We've been wanting to know who is going to play Thanos, who has a considerable supporting role in Marvel's 'Guardians of the Galaxy' and is the overarching big bad of the Marvel Cinematic Universe, since his first appearance in the 'Avengers' post-credits scene. Heck, we even wrote a whole article trying to figure out who is playing Thanos. At the time, we theorized that Vin Diesel was secretly cast as Thanos under the guise of Groot ("Why would he opt for just a smaller, supporting role with one line in a Marvel movie, when he could be playing the major villain behind a series of films?") But, now 'Guardians' director James Gunn says that's not true and we're right back to square one.

During the 'Guardians of the Galaxy' fan Q&A on Facebook yesterday, one fan did God's work and asked Gunn straight up who would be playing Thanos. Here is what Gunn had to say, emphasis his:

You'll have to wait and see. BUT IT IS NOT VIN DIESEL. He is Groot.

We don't think Gunn is pulling a J.J. Abrams/Khan on us, so we'll take him at his word and scratch Diesel off our list of prospective candidates. But, Marvel president Kevin Feige admitted publicly that Thanos HAS been cast, but that he's "not sure we want to announce it yet."

We'll revert back to our original list speculating on the casting and examine the one name on that list that's left: Benicio Del Toro.

Yes, Del Toro has already been cast as The Collector, but if Gunn and Feige are being this protective over a casting announcement, we have to think that the casting itself would reveal a major plot point/twist in 'Guardians' - namely that The Collector is secretly Thanos in hiding. We know Del Toro signed on for multiple Marvel movies and given his ominous "One down..." statement in the 'Thor: The Dark World' post-credits scene, he's obviously in 'Guardians' to collect the Infinity Stones.

Now, it could be that Marvel has just found a really cool actor to play Thanos and they don't want to give it away. But, in this modern era where everything leaks eventually, we'd be shocked if even Marvel was able to keep a major actor's participation in their big superhero movie a secret. Which means, the actor would have to be someone that's already on set and wouldn't arise suspicion.

What do you think? Are you disappointed that Vin Diesel is not playing Thanos? And, if he's not, what other major role was Diesel teasing when he said he met with Marvel about "a film that would be introduced in Phase 3...not for a few years"?

'Guardians of the Galaxy' opens in theaters on August 1.

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