The Silurians and Sea Devils are two fictional related ancient species created by Malcolm Hulke for the 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 has 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.

Doctor Who is a long-running British science-fiction television series that began in 1963. It stars its protagonist, The Doctor, an alien who travels through time and space in a ship known as the TARDIS, as well as their travelling companions. When the Doctor dies, they can undergo a process known as "regeneration", completely changing the Doctor's appearance and personality. Throughout their travels, the Doctor often comes into conflict with various alien species and antagonists.

The Silurians and Sea Devils are a race of reptilian humanoids from the dawn of time. The species was highly technologically advanced, and their computers detected that a planet-like object would collide with Earth. To survive, they put themselves into hibernation, but as the planet-like object, the Moon, never crashed into the Earth, the Silurians' computers never awoke them, leaving them trapped in hibernation.

In their first appearance in Doctor Who and the Silurians (1970), a group of Silurians are awakened from hibernation by the energy from a nearby nuclear power research center in Derbyshire. The Third Doctor (Jon Pertwee) initially manages to negotiate an honourable compromise with the colony's leader. Unfortunately, the colony's leader is murdered by a younger Silurian who becomes the new leader, intent on a far more aggressive policy. To that end, the Silurians then attempt to reclaim the planet from humanity by releasing a deadly bacteria and attempting to disperse the Van Allen radiation belt. Both plans were thwarted by the Doctor. Despite the Doctor's best efforts to broker a peaceful solution, the Silurians are still determined to exterminate humanity, resulting in Brigadier Lethbridge-Stewart (Nicholas Courtney) blowing up their base to stop their plans.

In The Sea Devils (1972), the Sea Devils, an amphibious variety of Silurians, are awakened from their hibernation by a renegade Time Lord known as the Master (Roger Delgado), who persuades them to reclaim the planet from the human race. Despite the Third Doctor's efforts to convince them otherwise, the Sea Devils eventually decide to go to war, forcing the Doctor to destroy their base. It is revealed, however, that there were many colonies still in hibernation around the world. Both species, together, in "Warriors of the Deep" (1984), attempt again to reclaim Earth from the humans. Set in the year 2084 during a prolonged "cold war" between factions of humanity, the pair attempt to fire an undersea base's nuclear weapons, which would cause the humans to destroy each other in retaliation for the initial strike. The Fifth Doctor (Peter Davison) attempts to make peace with them, but is unable to, forcing him to flood the base with hexachromite gas to stop them. While he attempts to save the Silurians, he is unable to succeed, leaving all of them dead by the serial's end.

Silurians are reintroduced to the series, following its cancellation and revival, in the 2010 two-part story, "The Hungry Earth" and "Cold Blood", in which Silurians are awoken in 2020 by an underground drilling operation. Having misinterpreted the drilling as a deliberate attack, the Silurians take hostages. After a protracted conflict, the Eleventh Doctor (Matt Smith) leaves behind Tony Mack (Robert Pugh) and Nasreen Chaudhry (Meera Syal) in the Silurian city to act as ambassadors to the human race when they re-awaken in a thousand years.