Silurian and Sea Devil

The Silurians and Sea Devils are two fictional related ancient species created by Malcolm Hulke for the long-running British science fiction television series Doctor Who. The Silurians are a race of scientifically advanced reptilian humanoids from the dawn of man which first appeared in Doctor Who in Hulke's 1970 serial Doctor Who and the Silurians. The Sea Devils are similar to the Silurians, but hail from the oceans and are aquatic, having debuted in the serial The Sea Devils (1972). Both species then reappeared in the 1984 serial Warriors of the Deep, which was the final appearance of both races prior to the show's cancellation in 1989. Following the show's revival in 2005, heavily redesigned Silurians were reintroduced to the series in 2010, and have recurred frequently since then. The Sea Devils were reintroduced in 2022, with their designs mostly unchanged.

Working under producer Terrance Dicks, Hulke came up with the idea of the Silurians to accommodate the show's need for more imaginative science fiction storylines during a period when its title character, the Doctor, was confined to present-day Earth. The Sea Devils were made out of a desire to bring the Silurian concept back. The further re-appearance of the pair in Warriors of the Deep was done out of a desire to bring back more antagonists following the series' twentieth anniversary. The species' redesign and re-appearance in the revived era was done to bring out the humanity in the species and allow the actors' performances to shine through, with a desire to update the Silurians to modern-day standards and expand on the concepts introduced in their original serials. Conversely, the Sea Devils' return did its best to stay as loyal to the original design of the creatures as possible.

The Silurians and Sea Devils' concept have been highlighted, though they were considered largely forgotten monsters until the Silurians' return in the revived era. In 2018, the notion of a pre-human intelligent reptilian or amphibious species was explored by the real-life scientists Adam Frank and Gavin Schmidt, who dubbed the concept the "Silurian hypothesis". The Sea Devils are set to play a major role in the spin-off series The War Between the Land and the Sea.