10 Deadliest Doctor Who Villains
2. The Master
While Davros is evil to the core, the Master represents a threat far deadlier to the universe. As a Time Lord, the Master has the ability to regenerate, and this has kept them as the Doctor's oldest enemy for the better part of their lives. Sadly, they're also the Doctor's oldest friend.
Unfortunately for the Master, they're completely and totally insane. Despite this infirmity, they're a genius on par with the Doctor's intellect, but because they're chaotic evil while the Doctor is chaotic good, they have become the Doctor's antithesis. Where one is good, the other is pure evil, but neither wants to completely destroy the other.
In many ways, the Master is a relatable character, and no, you don't have to be a lunatic to understand their point of view. Whatever horrific acts the Master undertakes, there's a reason behind them, and in that way, it's at least possible to understand them.
That being said, they've routinely killed untold millions, and possibly billions through their villainous plots. They will kill without hesitation or reason, or they won't. It depends on their mood at the time. Regardless of their many crimes, the Doctor has consistently been unwilling to destroy their nemesis.