Cybermen

The race originated from the planet Mondas. They were originally a wholly organic species that eventually adapted cybernetic implants to such a degree that it began to affect their minds. Emotions were largely abandoned outside of naked aggression and the Cybermen became a race of conquerors who reproduce by taking other organic beings and forcibily converting them into cybermen in facilities called 'Tombs'.

Their major weakness is the element, gold, which can fatally interfere with their life support systems.

The cybermen also used small metallic insect-like creatures called 'cybermats' as weapons of attack.

In many ways, the Cybermen can be seen as a more individualistic precusor of Star Trek's major enemy, The Borg.