Doctor Who is no stranger to bizarre monsters and unusual dangers. After thirteen incarnations (even more if one includes Peter Cushing, Richard E. Grant, and Rowan Atkinson) of wandering around space and time, it's hardly surprising that the Doctor has encountered their share of enemies in both the original and revived series. His opponents have ranged from cruel warlords to misunderstood creatures to eldritch monstrosities.

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Occasionally even humans can become the biggest threats. The Doctor has several recurring enemies that are well-known to fans: Daleks, cybermen, sontarans, along with a few more obscure ones like the autons and ice warriors. The classic Doctor Who series has its share of strange monsters, some of which have been brought back for the revival. But there are a few who tend to stand out.

5 The Captain

Doctor who the Pirate Planet Captain

Few of the Doctor's enemies were quite so memorable or entertaining as the one introduces in Season 16. The Pirate Planet introduced the space pirate known as "The Captain" who took the concept of space piracy to a whole new level. The character's design is perfect, from the cybernetic headset with an eyepiece resembling an eyepatch to a curious stretch of metal that gives the illusion of a mustache. He even has a robot parrot to help reinforce that he is indeed a pirate.

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Ironically, for someone who commits some pretty serious atrocities, trapping entire worlds in his hollow planet and mining them until all that remains is a fragment just big enough to keep as a trophy (and coming dangerously close to doing that to Earth), The Captain is a strangely entertaining character. He has a way of stealing the show whenever he appears on screen, and actor Bruce Purchase really seems to have fun with the role. It actually becomes hard to see him die at the hands of a much more dangerous (and less charismatic) antagonist at the story's conclusion.

4 Davros

Doctor Who Davros Genesis of the Daleks

Daleks have been a staple of the series since the beginning, making their first appearance literally in the second-ever episode and becoming a hit with viewers, so much so that the BBC would continue to bring them back again and again. Every Doctor has faced the Daleks at least once. These biomechanical tanks are genetically modified for one purpose- killing everything that is not them and sometimes even killing each other.

1975's Genesis of the Daleks introduced fans to the twisted scientist behind their creation. Davros was a genius, with no sense of morality, which is a dangerous combination. He was the kind of scientist who viewed morality as a barrier to progress and was happy to experiment on unwilling test subjects in ways that would make General Deathshead cringe with fear.

Even worse is his obsession with not only building but also perfecting the Daleks. This is a man ready to arrange the extinction of his entire race just to keep his project from being shut down, and who would not give up even after being betrayed by his own creation. It actually makes him worse than the monsters he created.

3 Krynoid

Doctor who the Seeds of Doom Krynoid

Long before John Carpenter's The Thing, a very different alien parasite came out of the Antarctic in Doctor Who's season 13 episode The Seeds of Doom. It's the Krynoid, an alien plant with a history of overtaking entire worlds and reproducing by spreading pods through space.

These pods are capable of surviving in a vacuum and being frozen until a perfect host arrives. Once a person is infected they are quickly transformed into a humanoid plant monster that only exists to further the Krynoid's will. The more it infects, the more powerful it becomes until it is unstoppable.

2 The Master

Doctor Who the Master Cropped

The Doctor had many recurring enemies, but few were as close to his intellect as "The Master." He has gone through a number of iterations in both the original and revived series, being played by several actors over the years who all have a unique take on the character. The same traits, however, continue to reappear: unpredictability, ruthlessness, and an uncanny ability to escape from almost certain death. Not even old age was enough to end him.

While he has come back for the revival, the Master was a much bigger part of the classic series. He was a regular nemesis of the Third Doctor and a frequent opponent from the Fifth Doctor onwards. He had two main iterations: Roger Delgado and Anthony Ainley, with two actors in between.

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Roger Delgado's is undoubtedly the best. Not only is he cunning, but he is also a master of chess and manipulation. He expresses his contempt for humanity through a variety of blatant aliases (i.e. "Colonel Masters") and knows how to turn any situation in his favor. He also has an advanced form of hypnosis that can instantly turn anyone into his personal slave.

1 Rutan

Official image of the Rutans, an alien from the TV show Doctor Who.

Every Doctor Who fan knows the Sontarans, the warmongering clone race that has caused trouble for the Doctor since the John Pertwee era. Their brutality and willingness to do absolutely anything in the name of victory have made them frequent enemies in both the original series and the revival, and they even became major parts of the Flux storyline.

But what of their longtime nemesis, the Rutans? They have fought with the Sontarans for thousands of years, possibly more, in a seemingly endless conflict with both sides only willing to stop when the other is defeated.

Nearly every Sontaran story involves them trying to gain some advantage over the Rutans, but curiously the Rutans have only made an actual appearance in one episode: Season 15's Horror of Fang Rock. The episode shows that the Rutans are quite terrifying in their own right. The Rutan seen in Horror of Fang Rock was able to isolate a lighthouse and kill everyone inside in a matter of hours, and that was a single individual working with limited resources at a point where they were growing desperate.

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