The Proto-Indo-Europeans, sometimes simply called Indo-Europeans, were a prehistoric people or group of people who are thought to have spoken a language (or group of similar languages) which linguists have reconstructed as 'Proto-Indo-European', representing the ancestor of the modern Indo-European languages which were spread later across Europe and a part of Asia (mainly Iran and India). Proto-Indo-Europeans probably lived around 6-7,000 years ago.
See: Indo-European languages > Origins.