The Sontarans made their first appearance in 1973 in the serial The Time Warrior by Robert Holmes. There, it was explained that they are a race that reproduces by means of cloning . They live in a militaristic society obsessed by war. Sontarans are humanoid, with a squat build and distinctive dome-shaped head. They come from a high-gravity world named Sontar in the "southern spiral arm of the galaxy", and are far stronger than humans. They recharge their energy through a "probic vent" at the back of the neck rather than by eating food; they also use this vent in their reproduction process. The Sontarans have been at war with the Rutan Host for thousands of years. In the episode The Invasion of Time, the Sontarans successfully invaded Gallifrey , but were driven out again after less than a day.
Although physically formidable, the Sontarans' weak spot is the probic vent at the back of their neck; they have been killed by targeting that location with a knife and an arrow. They are also vulnerable to "coronic acid".
At some point, the Sontarans encountered the Rutan Host. The war between the Sontarans and the Rutans continued for several millennia, with both sides remaining fairly evenly matched and neither side interested in negotiating for peace. It was still ongoing at the time of The Sonataran Experiment, which takes place at least 10,000 years beyond the 30th century. The episode Horror of fang rock, set during the early 20th century, hinted the Sontarans had gained the upper hand, but this proved merely a temporary setback for the Rutan Host.
The Time Warrior(1973-1974): A Sontaran named Linx, trapped in the Middle Ages, uses crude time travel technology to kidnap scientists from the 20th Century to help repair his spacecraft.
The Sontaran experiment(1975): On a future Earth recovering from devastating Solar Flares, the Fourth Doctor,Harry Sullivan and Sarah Jane Smith discover Styre, a Sontaran warrior, conducting experiments on astronauts he has captured during their investigation of the rejuvenated Earth.
The Invasion of Time(1978):The Doctor returns to Gallifrey, having claimed the Presidency. His behaviour is unusual and has Leela thrown in jail. However, the Doctor is doing this to prevent a Sontaran instigated disaster.
The Two Doctors(1985):The Second Doctor and Jamie are on a mission for the Time Lords that goes horribly wrong, and Jamie sees the Doctor being tortured to death. However, if the Doctor died in his second incarnation, what does that mean for the Sixth Doctor and Peri?