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?
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, 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.
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.