There's no shortage of guile in the Marvel Cinematic Universe. When all has been said and done, some characters' plans and reactions are what make for some magical movie moments. Be it Nick Fury's backup plans or Tony Stark's mechanical trump cards, craftiness and self-preservation is a common thing in the MCU. It's the only way to survive a lot of the situations these characters get themselves into.
Suffice to say, Slytherins do exist in Disney's hand-crafted interpretation of the Marvel comic books. To reiterate, not all Slytherins are bad, but we'll be featuring some villains too. After all, their frequent displays of cleverness, leadership, resourcefulness, cunning, and ambition will have the Sorting Hat from Harry Potter giving them a one-way ticket to the silver-and-green elite club of Hogwarts.
10 NICK FURY
Nick Fury has proven time and again that he can be a devious schemer. He can even outwit more advanced aliens and manipulate the Earth's mightiest heroes like mere chess pieces. Moreover, his leadership in S.H.I.E.L.D. has proven to be a definite planet-saver.
Like any true Slytherin, no one can really truly know Fury's intentions, or sometimes even his allegiance. Despite being a conspicuous force of nature with a loud and colorful vocabulary, Fury still manages to be enigmatic and secretive.
9 RED SKULL
When it comes to villains, few humans in the MCU can match the inherent evil of the Red Skull (Johann Schmidt). Red Skull went on to create one of the most infamous and devious organizations in the history of comic books: Hydra.
For years, Hydra has been S.H.I.E.L.D. and Captain America's worst enemy. Their persistence, goals, and secrecy, commanded as per Red Skull's vision, can easily sum up everything bad in Slytherin. Heck, Red Skull even looks like a certain Slytherin who fashioned himself as a "Dark Lord," right down to the lack of nose!
8 BLACK WIDOW
Black Widow has arguably always been a Slytherin by heart, at least when it comes to the house's good traits. Her disposition for fraternity, stealthy nature, and opaqueness has put her in a similar light to Nick Fury. Both are difficult to read, are always switching sides out of self-preservation or an end that justifies the means, and they're also both spies.
Of course, in Avengers: Endgame, Black Widow showed her leadership qualities as well and her deep fraternal care for the Avengers. She's certainly a good example of what Slytherins can be if they choose to channel their traits to do positive things.
When you take a regular human and make him dedicated enough to try to take revenge against literal gods in the MCU, Zemo is the result. A victim of collateral damage thanks to Ultron's rampage, Zemo managed to devise an intricate plot to destabilize and disband the Avengers.
He did so by unearthing rotten buried secrets and setting the Avengers against each other through sheer craftiness. Such ambition could make even Harry Potter's Death Eaters green with envy. Come to think of it, Zemo was one of the sole reasons why Thanos ultimately won so easily.
6 THADDEUS ROSS
Another human with a huge ambition would be Thaddeus "Thunderbolt" Ross. He's a man who likes to solve his problems with huge weapons and as much brute force as he can. So, when Ross met a problem his usual tactic couldn't solve (the Hulk), he committed himself to find a way.
As a result, he's been a constant thorn in the Hulk's side ever since the two of them met. Ross' goal to bring down the big green monster is nothing short of tenacious. In addition, he basically acted as the harbinger of the Avengers' dissolution after bringing the Sokovia Accords down on them. Only a man of cunning and power like Ross could do that without angering the metahumans.
Loki cooks up lies and deception every single day for breakfast. Hence, he's a perfect Slytherin candidate. His favorite clothing color scheme even seems to match Slytherin's colors! When it comes to self-preservation, Loki is also quite a master himself and always finds ways to escape sticky situations to spread terror again another day.
It's even in Loki's nature to be mischievous and a schemer. Being a Frost Giant, Loki had to carve himself a place in Odin's family tree after Thor's father adopted him. Loki does tend to have a misunderstood and emotional side, but it tends to take a backseat to his scheming and ambitious tendencies.
4 HANK PYM
Also known as the original Ant-Man, Hank Pym is a dedicated but abrasive scientist. His colleagues don't always have the best opinion of him and he's also known to be highly distrustful of his friends, even Howard Stark. As a result, Pym mostly kept his big discovery, the Pym Particles, to himself.
One would think that such an invention could have been made to solve all the resource-related problems of the world but Pym, being a stalwart Slytherin, tends to value his achievements obsessively. Really, it wasn't until his successor Scott Lang came along that the Pym Particles were used for the good of the universe.
There's no contest here, no other Hogwarts House would take Ultron. Slytherin is where Ultron would feel most at home, especially since he tends to be murderous to "lesser creatures" every now and then. He and Voldemort would get along nicely.
In any case, Ultron's cunning, plans, goals, and even his narcissistic monologues all reek of Slytherin and their destructive traits. Ultron is hell-bent on achieving what he thinks is right. To that end, Ultron will stop at nothing trying to clear the world of humans.
2 DOCTOR STRANGE
Tony Stark was a candidate to be a Slytherin, but perhaps after that 'handy' stunt he performed in Endgame, he's more of a Gryffindor? A stronger Slytherin candidate could be Doctor Strange, who had the same vain tendencies as Iron Man before their transition into superheroes.
Strange was more condescending, more conceited, and more selfish than Stark, but his ambition and brilliance was undeniable. Moreover, his resourcefulness (especially with the Time Stone) is more than commendable and has proven to be a powerful weapon against cosmic threats. Thankfully, Strange learned some humility on his way to becoming a sorcerer.
Last but not least, it's one of the most 'Slytherin' characters in the MCU to date: Thanos. He basically nails the whole Slytherin trait checklist, both the positive and the negative. Thanos even gives Salazar Slytherin a run for his Galleons; they might as well rename the whole Slytherin House after the Mad Titan.
It's also worth noting that Thanos actually succeeded in his plans, mostly thanks to his Slytherin traits. Wiping out half your own universe's life forms is not something you can scoff at and makes Voldemort look distinctly small-time.