Voord

The Voord were a race of beings who had discovered how to resist the Conscience Machine on the planet Marinus.

History
The Voord, led by Yartek, sought to take control of the Conscience Machine, thus taking control of the planet, but were defeated by the Doctor, Susan, Ian and Barbara. (DW: The Keys of Marinus)

Later, the Doctor came into contact again with the Voord on the water covered planet of Kandalinga where they had enslaved the native amphibian species in hopes of using their labor to build enough dry land that the Voord could live on. From there the Voord leader planed to devise a way to return and take back Marinus. (DWA: The Fishmen of Kandalinga)

The Voords began experimenting with a World Shaper which came from a spacefaring civilization to accelerate time locally and "quick-evolve" themselves. Over time they replaced their body parts with cybernetic parts.

The Doctor, Frobisher, Peri Brown and Jamie McCrimmon attempted to stop the Voord. Jamie sacrificed himself to destroy the World Shaper, this caused a blast that accelerated time. Marinus became known as Mondas and the Voord evolved into entirely cybernetic creatures called Cybermen. (DWM: The World Shapers)


 * This last account conflicts with other accounts of the origins of the Cybermen.