10 Best One-Off Villains Classic Doctor Who Villains

10. The K1 Robot

Lumbering onto our screens in 1974's Robot, the Fourth Doctor's debut episode, the K1 was one of Doctor Who's biggest one-time baddies.

A prototype created by Professor Kettlewell of the National Institute for Advanced Scientific Research, it had originally been designed for mining and working in hazardous conditions. Under the instructions of Kettlewell, the K1 began a new task of removing pollutants from Earth - including humans.

Built from 'living metal' and armed with a disintegrator gun and huge claws, 'The Giant Robot' was a destructive force that tangled with UNIT, the newly regenerated Doctor, and Sarah Jane Smith.

Trying to reason with the robot, Sarah Jane found herself captured as it went on a rampage. Deciding to spare her because of her 'kindness', the robot began to develop some kind of Oedipus Complex - rebelling and killing its creator to protect Sarah Jane.

During an attack on UNIT, the Brigadier shot the K1 with the disintegrator gun which instead grew it to an enormous size. Now King Kong in scale and carrying Sarah Jane, the Giant Robot seemed unstoppable. With tanks inflicting no damage to it, it took the Doctor and a metal-eating virus to shrink it back down to size and save Sarah Jane.

An out of control robot with a killer conscience; this villain remains as one of UNIT's toughest and most memorable adversaries, with even the Tenth Doctor referencing its legacy in 2009's Planet of the Dead.