Khazar hypothesis of Ashkenazi ancestry

The Khazar hypothesis of Ashkenazi ancestry, often called the Khazar myth by its critics, is a largely abandoned historical hypothesis that postulated that Ashkenazi Jews were primarily, or to a large extent, descended from Khazars, a multi-ethnic conglomerate of mostly Turkic peoples who formed a semi-nomadic khanate in and around the northern and central Caucasus and the Pontic–Caspian steppe. (Wikipedia)