Voord

The Voord (also sometimes referred to as the Voords) were a race of semi-aquatic beings that tried to conquer many ocean planets, including Marinus, Kandalinga and Hydra.

Biology
The Voord usually wore a complete black bodysuit, which was similar to a frogman's wetsuit and flippers. 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. The Voord were also armed with commando-style knives.

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. Nevertheless, not all Voord had these cranial appendages. Yartek, the leader of the Voord on Marinus, only had two appendages, one on the right and left of his head. (TV: The Keys of Marinus)

Using these, 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 First Doctor's mind. If this organ was damaged or removed, the Voord would be rendered senseless. (PROSE: The Fishmen of Kandalinga)

The Voord mask fused with the wearer and usually could not be removed without killing them. The mask gave the Voord their telepathic abilities. Native Voord were given their masks in a ceremony when they achieved maturity. (AUDIO: Domain of the Voord)

On planets they conquered, the Voord converted the natives into Voord creatures by fusing them with Voord masks and suits — the mask tested their loyalty to the Voord, and if they were found disloyal, they were killed. While indistinguishable from the outside, unlike the native Voord of the Blood Tree, the converted Voord creatures had much less autonomy, and were mostly puppets of the native Voord commanders. The Voord suits lengthened their lifespans to a thousand years. (AUDIO: Domain of the Voord)

Technology
On Marinus, the Voord used one-man submarines, (TV: "The Sea of Death") 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 First Doctor believed them powered by anti-gravity. (PROSE: The Fishmen of Kandalinga)

History
A Voord expedition led by Yartek invaded the planet of Marinus. The Voord found a way to relieve themselves from the control of the Conscience of Marinus. They sought to take control of the Conscience, thus taking control of Marinus. They travelled to the island of the Conscience and killed the Keeper. When the First Doctor and his companions returned with the Conscience's keys, Ian Chesterton stopped them by handing Yartek a fake key, which destroyed the Conscience and killed Yartek. (TV: 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. (PROSE: The Fishmen of Kandalinga)

A hundred years after Yartek's defeat on Marinus, the Doctor encountered another group of the Voord, led by Overlord Tarlak and Commander Nebrin on the planet Hydra. Domain of the Voord)