Wikipedia
The Proto-Indo-Europeans were the speakers of the Proto-Indo-European language (PIE), a reconstructed prehistoric language of Eurasia. Knowledge of them comes chiefly from the linguistic reconstruction, along with material evidence from archaeology and archaeogenetics.
The Proto-Indo-Europeans likely lived during the late Neolithic, or roughly the 4th millennium BC. Mainstream scholarship places them in the forest-steppe zone immediately to the north of the western end of the Pontic-Caspian steppe in Eastern Europe. Some archaeologists would extend the time depth of PIE to the middle Neolithic (5500 to 4500 BCE) or even the early Neolithic (7500 to 5500 BC), and suggest alternative location hypotheses.
By the early second millennium BC, offshoots of the Proto-Indo-Europeans had reached far and wide across Eurasia, including Anatolia ( Hittites), the Aegean ( Mycenaean Greece), Western Europe ( Corded Ware culture), the edges of Central Asia ( Yamna culture), and southern Siberia ( Afanasevo culture).
Historically, earlier scholars often referred to the Proto-Indo-Europeans as Aryans, prompted by the belief that this was their original self-designation, or endonym, which the Proto-Indo-Europeans used in reference to their own ethnicity. However, only Indic and Iranian languages explicitly affirm the term as a self-designation referring to the entirety of their people, where as the same Proto-Indo-European root (*aryo-) is the basis for Greek and Germanic word forms which seem only to denote the ruling elite of Proto-Indo-European (PIE) society. In fact, the most accessible evidence available confirms only the existence of a common, but vague, socio-cultural designation of "nobility" associated with PIE society, such that Greek socio-cultural lexicon and Germanic proper names derived from this root remain insufficient to determine whether the concept was limited to the designation of an exclusive, socio-political elite, or whether it could possibly have been applied in the most inclusive sense to an inherent and ancestral "noble" quality which allegedly characterized all ethnic members of PIE society. Only the latter could have served as a true and universal self-designation for the Proto-Indo-European people.