Supposedly Ronan is seeking the Infinity Gems for Thanos. If he gets all the Infinity Gems then it threatens the entire universe.

The post-credits sequence of the last two Marvel films have teased not the immediate next film in that Cinematic Universe, but rather the one after that. "Thor: The Dark World" teased "Guardians of the Galaxy," while "Captain America: The Winter Soldier" teased "Avengers: Age of Ultron".

Therefore, the upcoming "Guardians of the Galaxy" should logically tease "Ant-Man". However, with that film delayed and probably not shooting before 'Guardians' is completed and printed, there's no real time.

So what might they do instead? Latino Review reports that they think another character will be teased during a post-credits sequence, one that could potentially be played by a familiar face.

POTENTIAL SPOILERS AHEAD

The site reports that the Human Rocket himself, Nova (aka. Richard Rider), will make an appearance. They can't confirm, but they guess he may be played by "Firefly" and "Castle" star Nathan Fillion.

Fillion has appeared in both of director James Gunn's previous features, so the inclusion isn't a big shock - especially as the actor already teased he makes an appearance in the film two months ago.

The report says the character will only be seen during the post-credits scene, and could be wearing a helmet so, like Thanos, he could be recast at some point down the road. The site hasn't gotten confirmation at this time as to the report's veracity.

Essentially Marvel's version of DC's Green Lantern (though there are differences), Richard Rider is an unsuspecting human who is recruited to become member of the intergalactic police force known as the Nova Corps. As a member of said force, he gains superhuman abilities.

I have been hoping for a Nova movie, so I hope that is true.

It will probably be awhile before we actually get it though. 2015 is Ant-Man and Avengers 2. 2016 is Cap 3 and Thor 3. Nova will be 2017 at the earliest.

Fillion has said on multiple occasions he wouldn't take a major role in one of these movies as long as Castle is running. Not sure how many more years that show has left in it, but I would guess at least 2.

He might do it just in the credits teaser with a mask on, but I don't think he would sign a multi picture deal with Marvel to play Nova permanently.

According to a mighty internet sleuth, Nathan Fillion will play Richard Rider in this summer’s GUARDIANS OF THE GALAXY. That’s right. After he was skeeted out of the Green Lantern gig (I love Ryan Reynolds, but he shouldn’t have been Hal Jordan) Nathan Fillion has a proper marquee role.

He’ll supposedly have a teeny tiny role in Guardians, but this will almost certainly lead to bigger and better things. If he doesn’t appear in Guardians of the Galaxy 2, then he’ll surely appear in some other cosmic movie. I imagine an Annihilation themed flick with intersecting Cosmic heroes. Minus Silver Surfer, of course, since he belongs to Fox Studios.

With DC’s own Justice League movie releasing in 2017, Marvel’s upping the ante. Nova’s obviously inspired by the Green Lantern Corp, so by introducing a fan favorite like Fillion as the lead so much sooner than WB’s rebooted Hal Jordan, Marvel claims influence over the whole ‘outer space superhero cops’ genre. After all, the fickle world of general movie goers only have room in their heart’s for one interstellar detective, and supposing Marvel Studios delivers a compelling Fillion Nova, they’ll easily claim masses.

Fillion is in the movie as a "small cameo"

Vance Astrovik?