The Fendahl were a gestalt organism, from the original fifth planet of the Sol system. They were composed of two parts, a Fendahl Core and the Fendahleen. The Fendahl posed a threat to all life, and when one Fendahl Core and twelve Fendahleen coexisted they had the power to destroy all life on a planet.
Thirteen physically separate organisms made up the Fendahl.
Fendahl Core, The skull of the Fendahl Core which transported itself to Earth resembled a human skull in every respect, but for a pentagram shape in the forehead, visible only by an x-ray. After her transformation into the Fendahl Core, Thea Ransome appeared as a golden-skinned, majestic being with gigantic, unblinking eyes.
Each Fendahl Core had twelve Fendahleen, large eyeless and limbless creatures with a fringe of pink tentacles around and two large fins above their mouths. They were difficult to destroy, but well-aimed bullets would kill them.
The Fendahl could drain all the spectrum of energy from their prey, or 'suck out their souls'. Even the skull nicknamed Eustace, the fossil remnants of a Fendahl Core twelve million years dead, had the power to drain the life force of The Doctor. The Core could create these Fendahleens from living beings with the correct genetic inheritance and in some cases could create the Fendahleen out of pure energy.
If the Core was destroyed, the Fendahl was killed. All of the parts of the Fendahl can telekinetically control people, but the Core has many more psychic powers such as mind control and astral projection.
The Fendahl and the Time Lords of GallifreyEdit
Roughly 12 million years BC, the Fendahl evolved on the Fifth Planet, located between Mars and Jupiter. The Fendahl began to kill all life on the planet, including each other. When the Time Lords learnt of the danger that the Fendahl posed, they placed the planet in a time loop. They also removed all trace of the Fendahl from their records. However, the Fendahl survived and transported itself to Earth.
On Gallifrey, the Fendahl passed into legend. As a boy, the First Doctor heard stories about the Fendahl that caused him to fear it even as an adult.
The Fendahl and humanityEdit
The essence of the Fendahl lay dormant in the skull of the Fendahl Core. This skull was able to affect the development of humans in order to produce a species which it could use. The skull was eventually discovered by Dr. Fendleman in the 1960s by discovering a "sonic shadow" and tracing it back to its source. Fendleman found the skull fossilized in the lava of an inactive volcano in Kenya. Since, according to human archaeological theory, a twelve million year-old human skull should not exist, Fendleman deduced, correctly, that the skull must have come from space.
Thea Ransome was captured by a coven worshipping the Fendahl and transformed into a new Fendahl Core, which then attempted to create more Fendahleen. However, the Doctor killed these and in her weakened state the Core was unable to prevent him from destroying the building in which they were, also killing her.
The Doctor then takes the 'Eustace' skull and drops it into a supernova.