If the basis for a memorable hero revolves around the strength of their villains, then it’s safe to say that the Doctor of Doctor Who has that requirement covered. Battling numerous alien threats in their travels across time and space, the Doctor has come up against some of the most infamous extraterrestrial villains in all of science fiction, many of whom have gone on to earn a distinguished place in pop culture fandom. From mutated, genocidal cyborgs to alien assassins masquerading as ordinary statues, these villains have cropped up time and time again in Doctor Who, terrorizing the Doctor and his various companions from one decade to the next.

Daleks

Few villains are as closely tied to the Doctor as their mortal enemy, the Daleks. One of the Doctor’s oldest foes in both canonical and production history, the Daleks have proved a continuous thorn in the Doctor’s side since 1963. Known for their genocidal hatred of non-Dalek lifeforms and their shrill battle cry of “Exterminate,” these evil R2-D2 lookalikes may appear harmless on the surface, yet they’re anything but. Harboring an unwavering desire to rebuild the universe according to their twisted image, the Daleks’ ultimate goal for galaxy-wide conquest easily makes them the most frightening antagonist in Doctor Who (as well as one of the most persistent).

The Master

Every great hero has their polar opposite. For Superman, it’s Bizarro. For Flash, it’s Reverse-Flash. For the Doctor, it’s the scheming, power-hungry sociopathic Time Lord, the Master. An intellectual genius constantly plotting their way towards positions of power, the Master strives to obtain total supremacy over the universe, allowing him to dominate every life-form he views as inferior (which narrows it down to everyone). Once childhood best friends with the Doctor on their home world of Gallifrey, the Master’s personal relationship to this fellow Time Lord establishes him a fascinating counterpart to Doctor Who’s well-meaning protagonist, making every one of their reunions that much more meaningful and dramatic to watch.

Cybermen

In many ways, viewers can almost describe the Cybermen as the Doctor Who equivalent to the Borg. Like their later Star Trek counterparts, the Cybermen are genetically mutated cyborgs whose main mission is to transform every other humanoid creature into unthinking, unfeeling robotic monstrosities. Like their fellow Whovian enemies the Daleks, Cybermen possess little to any emotional bearing, going about their duties with machine-like precision and remorseless efficiency. Whether originating from Earth’s “twin planet” Mondas or an alternative version of the planet, every iteration of the Cybermen have displayed the same deadly desire to add even more unfortunate souls to their growing army–putting the species one step closer to total mechanical perfection.

Weeping Angels

If you ever happened to find yourself standing opposite a Weeping Angel, the last thing you should ever consider doing is looking away. Once known as “the Lonely Assassins,” at first glance, the Weeping Angels appear as simple stone statues that bear a basic resemblance to angelic creatures. Once you take your eyes off of them, though, the Angels are free to move about, converting themselves into speedy alien mercenaries who sap their victims’ energy, hurling them backwards in time. With their jagged fingers, crooked hangs, and stoney gaze, the Weeping Angels almost certainly rank among the most terrifying antagonists the Doctor has ever come up against in Doctor Who, haunting viewers to the very core every time they pop up on-screen.

Davros

Every heinous creation can be traced back to a single individual, whether discussing the nuclear bomb, holiday fruit cake, or the genocidal Daleks of Skaro. When it comes to the latter, the grand architect of the murderous alien cyborgs can be found in the form of Davros. A megalomaniacal Skaro scientist responsible who deliberately mutated his own species (the Kaleds) into the genetically advanced Daleks, Davros’ delusional attempts to conquer the universe rivals the Master’s own self-serving ambitions. As brilliant as he is mentally unhinged, Davros’ unsettling appearance alone is enough to send chills down even the most strong-stomached Doctor Who fans.

The Silence

Like their fellow NuWhu antagonists the Weeping Angels, the Silence rely almost entirely on physical perception for their main offensive weapon in Doctor Who. Menacing characters with their unsettling physical features, once an individual takes their eyes off of the Silence, they immediately forget they ever saw them in the first place. Influencing humanity for thousands of years by whispering suggestions into world leaders’ ears, the Silence make for a more unique Doctor Who antagonist in that their end goal is ultimately benevolent in nature. 

As the Doctor is destined to one day answer the age-old question (“Doctor who?) that could threaten the fabric of reality, the Silence have made it their mission to bring about the Doctor’s demise–thereby preventing the universe from collapsing in on itself. As helpful as that goal might be, the Silence’s religious fanaticism and the lengths they’ll go to thwart the Doctor makes them a species viewers shouldn’t ever underestimate.