Created as the darkness to S.H.I.E.L.D.'s light, Hydra is Marvel's most dangerous evil empire. They're a ruthless, power-hungry terrorist group who are led by sinister figures; often they use the most dangerous advanced science to serve their purposes. But who are Hydra, what is their history, and what do they stand for?

Who Are Hydra?

In the , Hydra is a ruthless terrorist organization that became associated with the Nazis under the leadership of the Red Skull. We first encountered Hydra in Captain America: The First Avenger, where we believed they'd been defeated. In a thrilling twist, Captain America: The Winter Soldier revealed that Hydra had become a "beautiful parasite" existing within S.H.I.E.L.D., manipulating humanity to the point where we would give up our freedom. Hydra has been a recurring threat in the films, with the believing they dealt Hydra a mortal blow in Avengers: Age of Ultron.

Head over to Marvel's , though, and you'll see the ground war between S.H.I.E.L.D. and Hydra. Season 3 revealed that Hydra is actually an ancient group who formed around the worship of the insane Inhuman Hive. Desperate for power, Hydra figures have aligned themselves with whoever they believed would give them a chance to bring their 'god' back to Earth - and that's where they allied with the Nazis back in the Second World War. Although Hydra finally succeeded in bringing Hive back to Earth, a major defection gave S.H.I.E.L.D. the chance to crush them, and Hive ultimately died in space.

Enter The Framework

Agents of S.H.I.E.L.D. Season 4 culminated in an arc known as "Agents of Hydra," with the team plunged into a digitally-created virtual reality in which Hydra triumphed. Created by the arcane science of the Darkhold, the Framework was a madhouse-mirror version of the MCU, one in which heroes are villains and friends became foes. It was all ruled over by Madame Hydra, a twisted version of the artificial intelligence known as Aida.

As "Agents of Hydra" built to a climax, the boundaries between Earth and the Framework became ever thinner. Madame Hydra was committed to the ominous Project Looking Glass, which allowed her to create a flesh-and-blood body in the mainstream MCU!

What About The Comics?

A moment that shook the Internet! [Credit: Marvel Comics]
A moment that shook the Internet! [Credit: Marvel Comics]

Over in the comics, Hydra has continually been portrayed as one of Marvel's most dangerous threats. That's never more the case than in the last year, which has seen Steve Rogers's mind rewritten by the power of a living Cosmic Cube. Shockingly, Captain America himself has become Hydra's most successful double-agent, and has gradually risen to power in the ranks of Hydra. It was certainly a controversial plot-thread, with writer Nick Spencer and Executive Editor Tom Brevoort both receiving some chilling death threats.

It's all built up to this year's Summer Event, , which has seen Steve Rogers launch a devastating attack on the world's superheroes. By all accounts, "Secret Empire" is a sort of 'last hurrah' for Marvel's recent spate of politically-aware plots, with the publisher taking a step back from such divisive approaches as a result of poor sales.

Are Hydra Nazis?

Nick Spencer's Captain America twist was controversial for one simple reason above all others: to most of the world, Hydra are Nazis. In fans' eyes, Marvel has just made Captain America - the man who famously socked Hitler in the jaw - a Nazi. Adding to the controversy, the solicits and variant covers for Secret Empire #5 hint that even Magneto will ally with Hydra. Although Magneto is traditionally portrayed as an villain, it's worth noting that he's a Holocaust survivor who's shown nothing but contempt for Hydra in the past. Fans were furious at this act of perceived character assassination.

But are Hydra really Nazis? Nick Spencer has argued otherwise, and Secret Empire #0 went to great lengths to show the ancient history of Hydra. It's clear he views Hydra as fascist, but not strictly Nazi. Unfortunately, I rather think that ship has sailed; Captain America: The First Avenger and Captain America: The Winter Soldier both portrayed the terrorist group as Nazis. Given the films reach a wider audience than the comics (or even the TV shows), most fans view Hydra as Nazis, leaving Spencer struggling to defend the arc.

Even Agents of S.H.I.E.L.D. has joined the debate, with Simmons confronting a rebellious student in the Framework reality. Her view is simple:

"Hydra are Nazis. Every last one of them!"

Given that the character has essentially become the team's conscience and moral voice, when Simmons makes that kind of judgment - it's pretty hard to disagree.

Whether you view Hydra as Nazis or not, though, they're the ultimate Marvel villains - the darkness to S.H.I.E.L.D.'s light, a recurring threat that's unlikely to ever truly be defeated. After all - cut off one head...