So here’s the thing about Hogwarts houses: you’re sorted when you’re 11 years old. The Evil Queen looks, on the surface, very Slytherin. Not just because she’s a villain, but because she tries – keyword tries – to be cunning and manipulative, and sometimes she even, very briefly, succeeds at it. However, as a child, or even a young adult, she was just about the furthest thing from a Slytherin – and by the end of the series, that’s once again the case. Young Regina from “The Stable Boy” can only belong to one Hogwarts house, in my mind, and that’s Hufflepuff.
Slytherins are ambitious. Cora, for instance, is a textbook Slytherin, and it seems to be a great disappointment to her that her daughter is not. Young Regina didn’t care about power or status. She would have rather run away with the stable boy than married the king. Her greatest goal in life was to be happy and be with someone she loved. Even after Daniel’s death, she repeatedly insisted that she didn’t want power and didn’t want to be queen.
Regina was surrounded by Slytherins. Her father was probably a Hufflepuff, but her mother was definitely a Slytherin. Her mentor was a Slytherin. Most of the other people she worked closely with were either Slytherins (Jefferson, Maleficent, Facilier) or had learned to use Slytherin methods (Hook). It’s no surprise, then, that she learned from them and started acting more like a Slytherin. Her manipulation of the genie in “Fruit of the Poisonous Tree” is classic Slytherin cunning, and she acts a lot like a Slytherin during the Dark Curse as well. However, she still seems more comfortable just throwing a fireball at her problems than trying to solve them with anything resembling subtlety. She’s learned a lot, probably most of it from Rumple, but he and Cora still use her as a pawn without her even realizing it throughout seasons 1 and 2. As the seasons go by, she gradually drops the Slytherin routine.
You could make an argument for Gryffindor or Ravenclaw as well. She’s certainly brave, and like I said, her preferred course of action usually tends to involve throwing fireballs at her problems. In season 2 and onward, she is willing to put herself in danger and even sacrifice her life to protect others. She is also one of the more intelligent characters, has a vault full of spell books, and while Rumple insists that magic is emotional rather than intellectual, Regina is often seen experimenting with potions or spells and trying to figure them out on an intellectual level. However, she’s also very dismissive of the Charmings’ heroic quests and Belle’s bookworm tendencies. She has some Gryffindor and Ravenclaw strengths, but they don’t seem to be what she values most, and again, they certainly weren’t what she valued most as a young woman, let alone when she was actually Hogwarts-age.
Her values are essentially those of a Hufflepuff, expressed in a straightforward way at first, then warped and twisted, and eventually turned back into something more benevolent again.
Hufflepuffs are hard-working and “unafraid of toil”. Regina, as a young woman, was willing to become the wife of a stable boy, accepting a future in which she would be a commoner and would have to work hard in order to survive. As the Evil Queen, she was relentless in her pursuit of Snow White. It was a horrible goal, and it led her to do horrible things to countless innocent people, but she was nothing if not hard-working and dedicated. Never at any point, from the earliest flashbacks to the end of season 7, has she been unwilling to do something because it was too difficult or too much work. Whether she’s doing something good or something evil, something for herself or for someone else, she puts everything she has into it.
Hufflepuffs are typically loyal. This is something Regina struggles with, but a big part of her happy ending is finding people she can trust/be loyal to/do right by, and earning their trust and loyalty in return. In the early seasons, she seems desperate for human connections and latches onto the worst people – namely, Cora in season 2 – because she feels isolated and rejected. She’s done nothing but hurt and antagonize the people of Storybrooke, but it still hurts that they don’t accept her, just as it hurt that they didn’t accept her as queen in the flashbacks. As time goes by, she ends up becoming very protective of Storybrooke and the people who live there, and by the time she takes on a leadership role again in seasons 5-6, her attitude has completely changed: instead of demanding that others be loyal to her, she’s determined to do right by them and to earn their respect. In season 7, she is completely willing to dedicate herself to a cause championed by a group of strangers in an unfamiliar realm out of loyalty to Henry, and her cursed persona is a sort of unofficial community leader who cares deeply about her neighbors and stands up to Victoria Belfry for their sake.
Hufflepuffs are also concerned with justice. Regina doesn’t really seem to understand the concept of justice and spends decades of her life seeking revenge against an innocent; however, she does seem to believe she’s delivering justice and even uses that word to describe what she’s doing. Over time, she ends up going just as far in the opposite direction, giving out second chances to anyone who wants one as well as several people who have no interest in changing their ways. However, this, too, comes from what seems to be a deeply ingrained need for fairness: she herself was given more than one second chance, so how can she deny the same to others? She frequently talks about what is and isn’t fair and at one point tells the Charmings that being a leader means doing what’s best for the greatest number of people. In the later seasons, once she is firmly on the side of the heroes, she frequently stands up to people whose actions she sees as unfair. For instance, she helped turn the trip to the Underworld into a mission to make things right and to help as many souls as possible resolve their unfinished business and move on. In season 7, she stands up to Victoria Belfry in large part because she is treating the people of Hyperion Heights (and her own stepfamily) unjustly.
Order of the Phoenix adds one final quality: “Said Hufflepuff, ‘I’ll teach the lot and treat them just the same.'” Rather than favoring only the students that shared her own strengths and values, Helga Hufflepuff also took the students rejected by the other three founders. Regina, in her earliest flashbacks, was willing to embrace Zelena as her sister even though she was a commoner and even though Cora warned her it would ruin their family’s reputation and her marriage prospects. In “The Stable Boy”, she wanted nothing more than to run away with Daniel, and her second love was an outlaw who lived in the forest and stole from the rich to give to the poor. She cared very little about people’s origins or status, and many of the people she cared about most were commoners. Likewise, unlike many of the show’s other magic-users, she’s never seemed to look down on those without magic, or to view them differently in any way. At one point in season 4, she tells Henry, “We are each given our own gifts. You have the heart of the truest believer. You brought us all together. Never think you’re ordinary just because you don’t have magic”.
Now, the original Pottermore welcome letter did say that Hufflepuff has produced the fewest dark wizards. However, few doesn’t necessarily mean none. I’ve put less-than-perfect characters in Hufflepuff before. Javert from Les Miserables takes hard work and obsession with justice to an unhealthy extreme, Edmund from Narnia grows to embody Hufflepuff virtues after making a very serious mistake as a child, and Seven of Nine from Star Trek: Voyager is loyal above all else, but (in the beginning) to the Borg, who want nothing more than to assimilate everything in their path. Regina is probably the most outright evil character I’ve ever put in Hufflepuff, but then again, she wasn’t always like that and develops into a much better person again over the course of the show’s seven seasons.