Apocatastasis

Apocatastasis, which can be translated as "universal restoration" is a concept that can be found in Ancient Greece. The theological idea was that people did not fully agree with their creator, and moved away; this is called Apostasy. At the end of time, everything would be re-united with its creator, according to the idea. Different people have seen the process differently: Some say, that everything, even those that have "fallen", will be reunited; these people speak about "apokatastasis panton" or "restitutio omnium (quae locutus est)". 
Ancient Greek philosophy used the term, before it was used by Christian scholars. That way, the Pythagoreans, Heraclitus, and the Stoics used the term. Neoplatonism, as well as Friedrich Nietzsche also used the term in this meaning. Most of these philiosophers believed, that this "restoration" was periodic, and not an event that occurred only once.
Clement of Alexandria, Origen and Gregory of Nyssa where the first Christian scholars who used the term: For them, this "restoration" would occur only once, and was not periodic.