An aggressive clone-warrior race from Sontar, who travel in spherical ships, the Sontarans were engaged in a war lasting many thousands of years with the Rutans. In pursuit of the advantage, Commander Linx of the Fifth Sontaran Battle Group tried to invade 13th century Earth, until repelled by the Third Doctor.
Later meetings with the Doctor saw the Sontarans invading the Time Lord home planet of Gallifrey, forcing the Sixth Doctor to build them a time travel machine, and trying to covert Earth’s atmosphere into one suitable for warrior cloning using the ATMOS machines. Sarah Jane Smith later encountered – and defeated – the last survivor of that invasion, Commander Kaagh.
A Sontaran by the name of Strax befriended the Eleventh Doctor and fought alongside the Time Lord and his allies at Demon’s Run. The diminutive warrior from the planet Sontar teamed up with Madame Vastra and a human by the name of Jenny Flint and accompanied the Doctor on numerous adventures.