Ultraterrestrials

""60 million years ago another race, superior to ours foresaw the catastrophe fled to space and fled the tragedy now they're here again, with a simple claim Alien, Alien attack They. Want. Their. Planet. Back.""

- S.P.O.C.K., Alien Attack

The ultraterrestials are an alien race that, well, isn't all too alien. In fact, they originate from Earth, just like us humans, but their civilization is so much older and more advanced than ours that they have no trouble hiding from us (for whatever reason). The term was coined by the ufologist John Keel in his Operation Trojan Horse in 1970, wherein he claims that the UFOs, various supernatural phenomena (like the Mothman), and religious myths imply the activity of an almighty High Energy Being co-existing with humans on Earth.

Contrast Earth All Along, which includes a reversal of this trope: human spacefarers encounter a strange planet with strange lifeforms. It turns out that a lot of time have passed, and this strange planet is actually Earth. Thus, the visiting human protagonists are actually Aliens From Earth.

Different from The Masquerade in that the masquerade is the act of hiding (e.g. in Men in Black extraterrestrials are walking among humans), whereas this is about the origin of the hiding species.

The ultraterrestrials often reside inside the Hollow Earth. Still others hang out in Atlantis, or a place that's said to be the inspiration for it. Compare/contrast Transhuman Aliens. Often a form of Precursor.

Anime

 * The Atlanteans in Nadia: The Secret of Blue Water.
 * The Olmecs in The Mysterious Cities of Gold.
 * The "Subterraneans" in Super Atragon.
 * The Dinosaur Empire (highly evolved survivors of when Phlebotinum Killed the Dinosaurs) in Getter Robo.
 * In the manga Outlanders, the invading aliens were originally from Earth. They were not happy to find squatters on the Sacred Mother Planet.
 * The title nasty in the Gorn-filled Hentai OVA series Demon Beast Invasion; numerous retcons gradually transformed it from an advance scout for his race to a transdimensional Cosmic Horror.

Comics

 * The Reveal in the 2000AD series  was that the Eldritch Abomination villains were actually a trio of Earth superhumans who had evolved far beyond human form and and gotten stuck on the wrong side of a dimensional barrier in the process.
 * Marvel Comics has the Eternals, the Deviants, and the Inhumans, all different groups who were genetically modified by aliens, long ago. Also the Sub-Mariner's Atlantis.
 * Lost lands of this type were also a staple of the company's "giant monster" and science fiction stories in the 50's, although not all of those stories are still considered canon in the Marvel Universe.
 * The DC Universe has Paradise Island/Themyscira, home of the Amazons; Gorilla City, home of gorillas genetically enhanced by aliens; and Aquaman's Atlantis. The Warlord's land of Skartaris used to count, being a Hollow World, but then got retconned as being a Land of the Lost-style Alternate Universe.
 * According to one story from Arion Lord Of Atlantis at least one alien race is descended from Atlantean space explorers. This might be an explanation for why there are so many human-looking alien races in the DC Universe.
 * Gold Digger LIVES on this trope. Digging up artifacts from such civilizations is the whole point of Gina's character.

Film

 * In the 2005 War of the Worlds film, the aliens had buried their war machines underground back before humans had evolved.

Literature

 * In Sinister Barrier by Eric Frank Russell, Earth is populated by Vitons, Energy Beings who exist outside visible spectrum and feed upon human pain and anguish. Oh, and when they die, they turn into ball lightnings.
 * In Bruce Coville's novel The Search for Snout, a boy believed his Disappeared Dad was an alien, but upon meeting him in space, finds out that he's a scientist from Atlantis who traveled into space before it fell, became immortal, and had adventures on alien worlds before returning to live. (And then he disappeared because an alien he'd ticked off on his adventures found him and wanted to harm his family.)
 * The fairies from the Artemis Fowl series have got magic and have technology 50 years ahead of ours. And they live within the Hollow Earth, to boot.
 * Humorous version from one of the spin-off Dilbert books, where Scott Adams postulates that all the smart people in the world have hyper-evolved to resemble grey aliens and are the real cause behind UFO sightings, but in fact have all just gone off to live in Switzerland.
 * In the writings of Richard Sharpe Shaver--which he and many others believed to be fact--the Earth was once home to a super-advanced race of people living in ancient cave cities who abandoned this world to travel to another, leaving behind their descendants, the noble Teros and the degenerate Deros. The Deros would later inspire the evil dwarf-like Derros in Dungeons and Dragons.
 * The dolphins in The Illuminatus Trilogy.
 * In Anne McCaffrey's Acorna series, the eponymous character is a member of a humanoid race of unicorns, descended from more traditional equine unicorns and the Sufficiently Advanced Aliens who rescued them from being hunted to extinction on Earth in the middle ages.
 * Ken MacLeod's Cosmonaut Keep series is set in the Second Sphere, an area of space colonized by successive waves of intelligent Earth-evolved life forms, starting with hyperintelligent giant squid, and uplifted dinosaurs. Who fly around in saucers and happen to look a lot like grays.
 * A staple of H.P. Lovecraft's Cthulhu Mythos. Deep Ones, Ghouls, and Sand Dwellers are all roughly humanoid and presumably originated on Earth; the Cthonians could also possibly be of terrestrial origins, but their being full-fledged Eldritch Abominations makes this hard to determine. The Great Race is actually a subversion, as while their host bodies originated on Earth, the possessing intelligences that are the actual Great Race projected themselves through time and space from elsewhere and -when.

Live Action TV

 * In the Star Trek: Voyager episode "Distant Origin", the starship encounters an ancient civilization of earth dinosaurs. However, the theory that dinosaurs originate on Earth quickly gets branded as heresy, since it conflicts with the dogma that they have always been in their current region of space.
 * The Doctor Who serials "Doctor Who and the Silurians", "The Sea Devils" and "Warriors of the Deep" feature various branches of a scientifically-advanced race of lizard people who ruled Earth in the days of the dinosaurs BEFORE the dinosaurs (stated at least once as being 300 million B.C).
 * Also, the Cybermen were originally humans. As of developments in the new series, there are now two distinct groups of Cybermen: those developed into Cybermen on Earth's twin planet Mondas and those created in an Alternate Universe (wherein Britain is a republic, Rose Tyler's dad is still alive, Rose Tyler never existed, and Mickey is Ricky).
 * There were even a few Dalek iterations that were fully or mostly created using human genetic materials (such as those from the finale of the first season of the new series). Being Daleks they were not amused by this fact being pointed out.
 * There was also the Fendahl, whose skull crashed on Earth long before humans existed and psychically guided human evolution for thousands of years so that it could have a suitable host.
 * The revived series does a purer form of this trope with the Silence,, but always went unnoticed due to the fact that you forget their existence as soon as they leave your field of vision.
 * Gary Seven, from the Star Trek: The Original Series episode "Assignment: Earth", was from a race of humans raised on another planet, returned to Earth to guide human evolution.
 * The aliens in X-Files were actually ancient native Earth lifeforms that left for a few millennia and decided to come back. Much to their horror, they found that those pesky apes had built a civilization and replaced them -- so they set out to re-colonize Earth, using the Government Conspiracy to aid them.
 * Fringe's First People
 * The antagonists in the Ultra Seven episode "Envoy from Nonmalto".

Music

 * In the song "Alien Attack" (see Page Quote), the synth band S.P.O.C.K. tells a story of hypertech dinosaurs coming back to reclaim their home planet from the humans.

Tabletop Games

 * The Subterrans and Tritons in Monsterpocalypse.

Video Games

 * The Lunarians in Touhou Project.
 * The D'ni of Myst fame, though they originated on another world. Their city can be visited in Myst V and URU.
 * In Iji the Komato, and, by extension, the Tasen originated from Earth.
 * The Gillmen of X-COM, possibly inspired by the Silurians and Sea-Devils of Doctor Who.

Web Comics

 * The dragons in The Inexplicable Adventures of Bob, although they left Earth for another planet in the Middle Ages.

Web Original

 * The ahuman and solipsist transapient AIs from Orion's Arm are ultraterrestrials to an extent - they were originally created by humans, but after losing their cyberwar against the pro-human transapients, they were exiled from Earth. When the (trans)humans and pro-human AIs finally reached the systems the ahumans had passed through, they found apparently alien artifacts - which turned out to be just stuff that the ahumans had built.
 * The SCP Foundation plays with this in the form of SCP-1000. They were the dominant species on Earth before humanity. Then humanity destroyed their civilization and wiped its own memory of those events through an unspecified means. Now the SCP-1000 want to be "let back in."

Western Animation
""Taste like crab, talk like people...""
 * Leela from Futurama was introduced on the show as a cyclops alien. As the series progressed, it was revealed she was a human mutant born on Earth.
 * South Park's Crab People.


 * Stingray: The various aquatic races.
 * The title monsters from Inhumanoids as well as the Mutores.