Within the wizarding world of Harry Potter and within the Hogwarts School of Witchcraft and Wizardry itself, all of the houses have certain stereotypes that people assume apply to everyone in a particular house. And this is the truest of house Slytherin, which has a (pretty unfair) reputation for being the "evil" house in Hogwarts.
The traits that make Slytherins so suitable for their house do tend to lean more "evil" than a lot of other houses though, so at the very least it's easy to see how a lot of traits like ambition and cunning could be turned into a negative more than a positive. However Slytherin, like every other house, has students and former students that are downright heroic. Plenty of Slytherins have done a lot of good for the wizarding world, and they usually don't get their due. So here we celebrate 10 Slytherins that actually did a lot of good for wizardkind.
10 Draco Malfoy
It took a lot for Draco Malfoy to outgrow his arrogant, prejudiced, and cruel behaviors, but he deserves a lot of credit for actually growing out of them eventually.
Malfoy experienced a lot of trauma once he went full-blown Death Eater and was assigned to kill Albus Dumbledore, and after his experiences, he made a drastic turnaround when it came to his feelings towards muggles and muggle-born witches and wizards. He and his parents had some tension between them because of his shift in philosophy, but Draco went out of his way to raise his own son to not look down on the people he had been raised to hate.
9 Phineas Black
Not much is known about Phineas Black the younger, except the fact that he managed to distinguish himself from his purity obsessed family when he stood up in support of muggle rights, which led to his father disowning him from the Black family. Phineas Nigellus Black was Phineas' father, and he has the dubious distinction of being the least popular headmaster in Hogwarts history.
Phineas Nigellus understandably hoped that all of his children would follow in his blood purity footsteps, but his eldest son and namesake rejected his father's views and became his father's greatest shame, and his rebellion certainly made the wizarding world a bit better.
8 Horace Slughorn
To be honest, Horace Slughorn was a self obsessed social climber who probably did more bad for the wizarding world than good, but at the very least he did eventually come clean about being the one who told Tom Riddle about Horcruxes, and if he hadn't done that then it's more than possible that Harry Potter wouldn't have been able to defeat Voldemort in the end.
Sure, Slughorn is the one who actually told him about Horcruxes in the first place, but Voldemort would have figured out how to make them one way or another, and for a man who was as vain as Slughorn it was a pretty big deal that he actually shared his most shameful moment with others for the greater good.
7 Narcissa Malfoy
Narcissa Malfoy is actually a pretty objectively terrible person, but bizarrely enough the greatest dark wizard of all time probably wouldn't have been defeated if it wasn't for Narcissa. Mrs. Malfoy seems to have little care for anything or anyone outside of her own family, and she's selfish and apparently has no qualms with practicing the dark arts if it will benefit her. But she really does love her family.
When Narcissa was poised with an opportunity to rat out Harry Potter and allow Voldemort to defeat Harry for good, she prioritized the safety and security of her son Draco over everything else, and she lied to Voldemort. Which ultimately resulted in Harry's victory and Voldemort's destruction.
6 Leta Lestrange
Like many other Slytherins, Leta Lestrange was a somewhat arrogant and selfish girl, and she didn't seem to have many friends during her time at Hogwarts. But despite the pitfalls of her personality, she was ultimately a much better and braver person than most other Hogwarts students.
When the only people that Leta seemed to truly care for in her life, Theseus and Newt Scamander, were in mortal danger because of Gellert Grindelwald, Leta chose to provide enough of a distraction for the two of them to escape, and she sacrificed her own life in the process. She certainly knew that her attempt to hoodwink Grindelwald would get her killed, but saving her friends was worth it for her.
5 Andromeda Tonks
The Black family is one of the oldest, most powerful, and purest wizard bloodlines in the entire wizarding world, and to say that they take great pride in that fact would be an understatement. So when a member of the Black family decides to defect in any way, the reaction towards them is quite harsh.
That was certainly the case for Andromeda Black when she decided to marry a muggle-born wizard named Ted Tonks. And as Nymphadora Tonks' mother, Andromeda and her husband Ted were also allied with the Order of the Phoenix, so clearly this Slytherin lass did more good for the wizarding world than most in the Black family.
4 Regulus Black
Sirius Black's younger brother Regulus seemed like he was more than willing to follow into the traditional Black family footsteps. He scorned anyone who wasn't a pure-blood wizard, and he was very enamored with the dark arts. And of course, when Voldemort first began his ascent to power Regulus was eager to join up with the rest of the Death Eaters and conquer the wizarding world on behalf of all dark pure-blood wizards.
However, apparently as he got closer to Voldemort things just got a little too real, and he decided to defect. When he left he also took one of Voldemort's Horcruxes with him, and he even tried to destroy it.
3 Severus Snape
Plenty of Slytherins have done some good for the wizarding world, and the house certainly gets an unnecessarily bad rap because most of its students will always look out for themselves above all else, but it's an undeniable fact that one of the most heroic wizards of all time was also one of the most famous Slytherins.
Severus Snape did a great job of pretending to be a dark wizard, but he ultimately just wound up playing one of the best long cons in history. He spent years pretending to be loyal to Voldemort, all the while undermining him and waiting for the right moment to strike where he could inflict the most damage on the dark lord, and inflict damage he did.
2 Salazar Slytherin
Salazar Slytherin certainly had some less appealing qualities as a wizard, but that doesn't negate the fact that he was one of the creators of the greatest magical school in the world. Salazar had some particular notions of how the wizarding world should look and he could be unfairly prejudiced against muggles and muggle-born witches and wizards, but even in his own warped way, he did want to protect his students at any cost.
Slytherin house has a definite negative reputation, but Salazar Slytherin created a house that allowed the witches and wizards who prized ambition and cunning to maximize their abilities and get the most that they could out of their education.
It's interesting that Slytherin has such a negative reputation among Hogwarts houses, because the wizard that has done the most for muggle-wizard relations was actually a Slytherin student.
Merlin is one of the rare wizards that is so famous and was so open about his magical abilities that he's famous within both the wizarding and muggle communities, and a huge reason for that is because he intentionally revealed himself to muggles in the hopes that the wizarding world and muggle world could eventually become one. And as a member of one of the King Arthur's court, he obviously did plenty for the wizarding world as well as the human one.