The Sontarans are a fiction extraterrestrial race of humanoids from the British science fiction television series Doctor Who, and also seen in spin-off series The Sarah Jane Adventures. They were created by writer Robert Holmes.
The Sontarans are a race of humanoids with a stocky build, greenish brown skin, and a distinctive dome-shaped head. Ross Jenkins in The Sontaran Stratagem describes a Sontaran as resembling "a talking baked potato" but The Doctor sticks up for the Sontarans by saying that, to them he looks like a pink weasel. Sontarans come from a large, dense planet named Sontar in the "southern spiral arm of the galaxy" which has a very strong gravitational field, which explains their compact stocky form. They also are far stronger than humans, although smaller.
Although physically formidable, the Sontarans' weak spot is the "probic vent" at the back of their neck, through which they draw nutrition. It is also part of their cloning process. It provides incentive to continue moving forward in battle since retreat would expose this area to their enemies. They have been killed by targeting that location with a knife (The Invasion of Time), a screwdriver ("Shakedown: Return of the Sontarans"), and an arrow (The Time Warrior). Even something as simple as a squash ball aimed at that point or contact by the heel of a shoe is capable of incapacitating them temporarily (The Sontaran Stratagem). They are also vulnerable to "coronic acid" (The Two Doctors).
In the episode The Poison Sky, it is revealed that the Sontaran Empire have been at war with the Rutan Host for more than 50,000 years, and which, at a time around 2008, they are losing. However, the war is still raging at least 20,000 years later, in the serial The Sontaran Experiment.
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Official Site: BBC
Links: Wikipedia- The Sontaran Tardis Index File Wikipedia- The Time Warrior