Kastrian

The Kastrians were an ancient race of silicon-based humanoids from the planet Kastria.

Biology
Kastrians are large humanoids with a rocky exterior and a large crystalline structure on their heads. They have some mental powers, such as telepathy and a type of mental attack (which require their rings to function). Kastrians have the ability to absorb radiation in order to regenerate their body, which allows them to regrow their entire body if they have enough energy. (DW: The Hand of Fear)

Technology
Though the Kastrians have a wide variety of advanced technology, most of this was invented by Eldrad. This includes the barriers on Kastria to protect it from powerful solar winds and also the base on Kastria. Even the Kastrians' silicon-based forms were themselves devised by Eldrad. Most of these advancements were either destroyed or degraded after Eldrad was killed.

Kastrians also have a special crystal (which is generally in the form of a ring) which stores everything about them. This crystal stores the DNA and memories of the Kastrian, which allows any remains to be regenerated perfectly with enough radiation. The ring can also control the minds of other creatures, making them help the regeneration process. Despite this, the ring can also pick up the physical traits of the people who touch it, causing changes in the Kastrian's form. (DW: The Hand of Fear)

History
The Kastrians are an ancient race from around 150 million years ago. Eldrad was one of the greatest scientist of the Kastrians, improving the lives of the Kastrians with his advancements. At this time the Kastrians knew of the Time Lords.


 * ''Eldrad claims the Doctor has a duty to assist him in returning home, which suggests that during the Kastrian's original lifetime the Time Lords had yet to adopt their policy of non-interference.

Unfortunately, Eldrad was a cruel ruler, and he attempted to create an army to conquer the universe. The Kastrians revolted and tried to stop his actions. He then destroyed the barriers protecting the planet, though the Kastrians led by King Rokon were able to capture him. Though the spaceship he was in was destroyed, the hand of Eldrad was blasted to Earth along with his ring. The remaining Kastrians were a doomed species, since the only option left was a miserable underground existence. The Kastrians elected to give up and destroy all of the memory-crystals in the race banks, stopping the regeneration of any Kastrians. (DW: The Hand of Fear)