Terileptil

Terileptils were a space-faring reptilian species well-known for possessing a great love for art and beauty which is matched only by their great love of war.

Biology
Terileptils were reptilian humanoids with scaly green skin, flat faces and wide mouths. They required Soliton gas gas to breath. (DW: The Visitation)

Technology
Terileptils possessed a highly sophisticated technology. Dependent on Soliton gas, they perfected atmospheric processors which could synthesize and release needed amounts of the gas into the immediate area, allowing them to function in alien atmospheres lacking this vital component. They were familiar with the fairly common use of vintaric crystals as a means of artificial lighting, and the use of holographic energy barriers. Terileptilan technology made heavy use of polygrite and highly charged power packs. They did not appear to have knowledge of time travel, but were certainly familiar with the concept. Terileptils were especially noted for their use of androids, as guards, soldiers, and servitors. (DW: The Visitation)

Culture
The Terileptils placed great value on beauty, using aesthetically pleasing designs even in weaponry. Even the Terileptilan language reflected the artistic and scientific sophistication of this species; to the untrained eye Terileptilan script looked very much like mathematical formulae. As a part of this highly refined culture the Terileptils esteemed certain vocations, such as that of mime and circus clown, very highly.

Terileptils were allied with the inhabitants of the planet Hakol in the Rifta system, for whom they mine tinclavic, a key source of which is found on the planet Raaga. Condemned criminals were conscripted to mine this mineral, overseen by android guards and wearing control bracelets. Severe facial scarring was a common feature of these conscripts, possibly due to the toxic nature of raw tinclavic ore. (DW: The Visitation)

History
In 102 A.D., the Terileptils were among the races who joined the Alliance. They came to Stonehenge and helped imprison the Doctor in the Pandorica in order to save the Universe. (DW: The Pandorica Opens)

As early as Earth's late Middle Ages, Terileptils mined tinclavic for the people of Hakol. A psychic probe from Hakol is known to have landed on Earth at this time, becoming briefly active centuries later in the year 1643 and again in 1984. (DW: The Awakening)

In 1666, the Doctor found a small group of escaped Terileptil criminals who escaped from the penal colony on Raaga, who had somehow managed to override their control bracelets, reprogram an android guard to help them, and steal a ship. The ship was caught in an asteroid storm crossing through Earth's planetary system. The ships' escape pod crashed outside a small village near Heathrow. An outbreak of plague was already raging in London, and the Terileptils began to genetically augment the plague bacteria, plotting to eradicate humanity and seize control of the planet. Their plot failed when the Doctor and his companions fought them in a bakery on London's Pudding Lane and a torch dropped during the scuffle, together with an overloaded Terileptil hand weapon, resulted in the Great Fire of London, which destroyed the Terileptils and their augmented plague bacteria (DW:The Visitation)

In 3375, the Adjudicator Terrell and The Master destroyed their homeworld using the Darkheart device. Aside from individual Terileptils who may have been elsewhere in the galaxy when this occurred, this act marked the end of an interplanetary civilization which was over two thousand years old, and was also one of the final steps in the Master's descent into darkness. (MA: The Dark Path)

Other references

 * Tegan and Nyssa saw a hallucination of a Terileptil projected by the Master to stop them. (DW: Time-Flight)
 * The Doctor had a nightmare in which he and Tegan visited Raaga and helped Terileptil slaves construct a time corridor and escape. (ST: CHAOS)