The Terileptils are a race of tall, colorful reptilian beings. Each Terileptil seems to be of primarily one color - green, blue and red have been seen - but some of their scales and ruffles have variations in hue. They breathe through gills on the side of the head, their hands and feet are like flippers, and their mouths are full of pointy teeth. Their great appreciation of art and beauty is offset by their equal love of war, and they are driven by a deep sense of honor. They arm themselves with conical guns that fire a green ray, and their script resembles mathematical formulae. Their native atmosphere contains soliton gas, which is volatile when mixed freely with oxygen.
Terileptils are technologically advanced. They have skills in genetic engineering, can construct solid energy barriers that blend in with their surroundings, and are skilled in the construction of androids. They use opening mechanisms on their doors which are activated when a hand is pressed to them. Terileptils also use a common form of lighting with vinteric crystals, which give the light a greenish hue.
The Terileptils encountered by the fifth Doctor, Adric, Nyssa and Tegan had escaped from Raaga, where they were to have been prisoners for life in the tinclavic mines. On Raaga they had been fitted with control bracelets made of polygrite which take over the mind and override fear. These could be rendered inoperable by removing the power packs. Following their escape from Raaga, their ship was damaged in an asteroid storm and caught in Earth's gravity. Two Terileptils made a base in London while the third established a base in the surrounding countryside. It took with it an android, programmed to protect, which could be disguised as Death and fired a purple ray from its hand. The Terileptil adapted the prison control bracelets to enslave the villagers, who had to concentrate on their thoughts in order to report to the Terileptil. They intended to wipe out humanity by releasing a strain of genetically-engineered bubonic plague, then using the Doctor's TARDIS to acquire more androids for service. Their android, however, was destroyed by a sonic booster constructed by Nyssa, and when their London base was set on fire, the Terileptils dissolved in the heat.
