Slytherin definitely doesn't have the best reputation out of all the Houses at Hogwarts School of Witchcraft and Wizardry. However, regardless of their negative PR image, it's impossible to deny that quite a few extraordinary and memorable witches and wizards wound up in the house of the snake.
Some of Slytherin's finest (or at least strongest) are powerful in the sense that they are naturally blessed with exceptional magical power, some are powerful because of their social status, and some are powerful because of things like their intelligence or ability to manipulate. But who are the most powerful Slytherins of all time?
Draco Malfoy
As a Malfoy, obviously Draco was quite literally born into power. And while he doesn't get an enormous amount of credit for it, he's actually quite a talented wizard. He squares off against the likes of Harry Potter on the regular, and he's at least good enough in school to become a prefect.
However, aside from those few advantages that Draco has, he's actually relatively powerless.
Narcissa Malfoy
Narcissa Malfoy, like most members of the House of Black, was also a Slytherin. And, given that she was born into one of the most powerful wizarding families in the world and married into another, it's safe to say that she holds a significant amount of sway over the wizarding world.
But, while she exists in the orbit of Death Eaters, she was never officially one of them, so her power is relatively limited, and her most powerful moment came when she simply lied to Voldemort.
Horace Slughorn
Clearly, given that Horace Slughorn became a professor at Hogwarts, he was a magically powerful wizard with a lot of knowledge and intelligence when it came to witchcraft.
But Slughorn was also an expert social climber. He recognized that making connections with other powerful magicians gave him more power, so he really went out of his way to cultivate a social network that greatly improved his influence in the wizarding world.
Dolores Umbridge
Unfortunately for nearly everyone in the wizarding world, Dolores Umbridge is one witch who actually did hold a lot of power.
She was a perfectly capable spell caster to be sure, but it's her position within the Ministry of Magic and at Hogwarts that really gave her the power she craved. Dolores was born into a fairly mundane magical family, but worked her way up through the Ministry and used her gained influence as a weapon against many.
Bellatrix Lestrange
Scarily, Bellatrix Lestrange was undoubtedly one of the more powerful Slytherins in the history of the House. As a Black, she was born into the same power that her sister Narcissa was, and her marriage to Rodolphus Lestrange only increased that reach within the wizarding world.
Given what she did to Neville's parents, it seems obvious that she's incredibly magically powerful, and most importantly, she was really Lord Voldemort's right-hand woman, which afforded her a great deal of influence.
Lucius Malfoy
Lucius Malfoy actually underwent more ups and downs than nearly any other character throughout the Harry Potter saga, and it's safe to say that there were moments where he was on the outs in the wizarding world in every way imaginable.
But still, he's a Malfoy, he's a very strong wizard, and he's one of the highest-ranking Death Eaters of all time, so he's in a stronger position than most Slytherins in history.
Salazar Slytherin
Surprisingly, despite the fact that he created House Slytherin and Hogwarts School of Witchcraft and Wizardry, Salazar Slytherin isn't necessarily the most powerful Slytherin of all time.
Yes, he was a hugely influential figure whose actions still impact the wizarding world today, however, some students who followed in his footsteps outdid him. And even more than that, while Slytherin did create Hogwarts, he was also pushed out by the other founders.
Merlin
Merlin obviously isn't just a legend in the wizarding world, but in the muggle world as well. While he clearly has no influence over the contemporary storyline, the fact that he is so well known and that he managed to make his way on to King Arthur's Court says a lot.
He was obviously an extremely skilled magician, but the power that he wielded over the world must have been unparalleled in his era.
Lord Voldemort
Lord Voldemort's life goal was to become the most powerful wizard of all time and to completely overtake the wizarding world and remake it in the image of his own ideals. And what's terrifying is that he nearly succeeded.
When it comes to his magical power, pretty much no one can compete with him. If that wasn't dangerous enough, the fact that he has hundreds of devout followers made him nearly unstoppable.
Severus Snape
On paper, Severus Snape could never even hope to compete with someone on the level of Voldemort. He's a master of potions and a pretty amazing spell worker in his own right, but his magical abilities don't come close to Voldemort, and clearly no one is worshiping the ground he walks on or even giving him basic respect in most instances.
And yet, Snape managed to outwit and outmatch the Dark Lord himself, and by virtue of that alone, he's the most powerful Slytherin in history.