The existence of the Proto-Indo-Europeans (formerly referred to as Aryans) was once argued purely on linguistic evidence, but recent analysis of DNA of the Yamnaya culture and related steppe cultures, demonstrates their genetic legacy on Indo-European cultures in a timeframe that matches the expansion proposed by linguists.
Most interesting of all, despite the fact these people started off in the Pontic Caspian steppe of Eastern Europe, modern populations in all of Northern, Central and Eastern Europe all have a strong genetic affinity with them.
This video explains what genetic and linguistic evidence tells us about how they lived, what they looked like and what their pagan religion was like.