Ultraterrestrial is a term coined by John Keel, in the 1970s, to refer to technologically and scientifically advanced sentients who supersede human civilizations.
Ultraterrestrials are said to be living amongst humans since the dawn of time. Unlike extraterrestrials, they do not come from another star system, but rather from Earth. They may either be a different branch of biological evolution, or a certain human culture that unexplainably has evolved much faster than others.
John Keel has relied on the theory of ultraterrestrials to explain the mystery airships of 1896.