No doubt some of the craziest scenes in X-Men: Days of Future Past involve the mutant-hunting Sentinels. They're probably some of the fiercest villains we've ever seen in a superhero movie, mainly because they're giants capable of tearing off body parts and vomiting fire. Even when you manage to somehow defeat one, they keep coming. And man are they scary.

Now that the film is in theaters, Framestore has released some of the Sentinel concept art it created for the movie, revealing a variety of different looks for both the future and 1970s versions. Before we get to them, though, let's start with Jack Kirby's original design for the Sentinels, if only to see how they've evolved over the years.

Some more info on the Sentinels from our Marvel expert, John Gholson: "The giant robots made their first appearance all the way back in 1965's X-Men #14, from the all-time classic Marvel creative team of Stan Lee and Jack Kirby. Kirby's original design is impressive; you barely even notice that the robots are a pleasant shade of purple and pink while they're trying to murder you. The threat is in their faces. The off-putting, almost skull-like expressionless faces are scary enough to have even nonmutants shaking in their boots. Their purpose is to kill mutants, and they certainly look like killing machines. You'd never mistake them, for instance, for hugging machines."

Sentinel concept art from Framestore. Click to enlarge.

Updated with additional concept art, courtesy of Maciej Kuciara (Guardians of the Galaxy), via CBM.

And here's what they looked like in the film:

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