The Dál Cais was a significant Gaelic dynasty in medieval Ireland, primarily located in the region of Thomond, which is now part of County Clare. They were known for their influence and power during the 10th to 12th centuries, particularly under the leadership of notable figures like Brian Boru, who became the High King of Ireland. The Dál Cais were descendants of Cais, a legendary figure, and they played a crucial role in the political landscape of Ireland. Their legacy includes contributions to Irish culture, language, and the establishment of various clans, which shaped the history of the region.