Voord

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

Biology
Exactly what Voord looked like was unknown, as they were always seen in a complete body suit. This suit tended to be effective protection from hostile elements. It was not, however, completely impermeable. Barbara once discovered an empty Voord suit with two puncture marks, suggesting that the acid had consumed the Voord within.

Still, the shape of the suit suggested a few things about basic Voord anatomy. They were, for example, humanoid. And they had three appendages on their heads — a thin stick with a circle at the front and two loop-like horns on the side. (DW: The Keys of Marinus)

Using these organs, the Voord were capable of telepathically communicating with each other. The leader had the higher intelligence and was able to control others with this organ. They could also control the minds of the Fishmen, but they could not read the Doctor's mind. If this organ was damaged or removed, the Voord would be rendered senseless. (DWA: The Fishmen of Kandalinga)

Nevertheless, all Voord did not have all these cranial appendages. Yartek, the leader of the Voord on Marinus, only had two appendages, one on the right and left of his head. The Kandalinga incident notwithstanding, the precise functionality of each of these three appendages — and whether they were biological or technological — was unclear. It was therefore unknown whether Yartek represented a subspecies of Voord, or whether he merely had a different instrument panel in the helmet to his suit.

Technology
On Marinus, the Voord used one-man submarines, (DW: The Keys of Marinus) while on Kandalinga the Voord used large barges to travel around on. The barges travelled above the surface of the water and were capable of stopping and speeding up quickly. The barges made no sounds and no waste-products and the Doctor believed them powered by anti-gravity. (DWA: The Fishmen of Kandalinga)

History
The Voord, led by Yartek, sought to take control of the Conscience of Marinus, thus taking control of Marinus, but were defeated by the Doctor, Susan, Ian and Barbara. (DW: The Keys of Marinus) A few hundred survivors were able to escape, take two of the keys of Marinus, and make their way to Kandalinga. As there was no land to build on, they were forced to rebuild their ship into a base and enslaved the Fishmen as workers. They planned to convert the oceans to land and build ships to return to Marinus, a plan that would take thousands of years to complete. (DWA: The Fishmen of Kandalinga)

The Voords on Marinus began experimenting with a World Shaper, which accelerated time locally and "quick-evolved" the Voords. 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, which 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.

Many thousands years later, the Doctor came into contact again with the Voord on Kandalinga. After being brought to the leader, the leader believed that the Doctor's ship could be used by the Voord. The Doctor was able to stop the leader, breaking his telepathic control and allowing the fishmen to rise up and take back their planet. (DWA: The Fishmen of Kandalinga)

Professor Thripsted believed that the Voord were the direct ancestors of the Remote, and their entire planet a sociology experiment done by Faction Paradox, as outlined in Genetic Politics Beyond the Third Zone. (EDA: Interference - Book Two)

Other References

 * When a museum was made from the Doctor's memories in the Matrix, it contained a Voord mask. (IDW: The Forgotten)
 * Iris Wildthyme was said to have fought Voords in the Death Zone. (PDA: Verdigris)

Behind the scenes
Based entirely upon the their televised appearance, it would be possible to believe that the Voord were not necessarily a species at all, but merely a cultural grouping of Marinusians. Arbitan tells Ian Chesterton, "The man who just attacked me was a Voord." Later, he also describes Yartek as "a man named Yartek". Philip Hinchcliffe's novelisation seeks to make things clearer, by changing the language to, "The creature who attacked me was a Voord," and by referring to Yartek as a "Voord named Yartek".