10 Deadliest Doctor Who Villains
3. Cybermen
The Cybermen are a race of perfectly engineered cybernetic humans, or at least, that's what they believe they are. Wherever or whenever a new breed of Cyberman arises, they become a singular threat to all of humanity, and intergalactic wars between them and humans have resulted in trillions of casualties.
In order for a Cyberman to be made, a human must undergo an "upgrade," which is a process that mutilates the body and mind. The result is a mostly inorganic being with some organic bits (like the brain) remaining inside. The real transformation comes from the complete inhibition of emotions.
When a human's emotions are turned off, they have no problem laying another person down to be upgraded, so it is impossible to reason or bargain with them. They see themselves as superior, and the only thing to do with a human is to upgrade them to their idea of perfection.
Becoming a Cyberman effectively kills the human, so for every Cyberman, there's at least one person who had to die to bring them into the universe. They are one of the deadliest enemy races in all of the Doctor's history, but despite their seemingly incalculable body count, they aren't the deadliest...