The kings of Dál Riata have their genealogy traced back through the king lists and annals to Domangart mac Fergusa, who lived in the early 6th century. His father, Fergus, is considered semi-legendary. This far back, the genealogies found in the annals (like The Annals of Tigernach and the Annals of Ulster) are mostly things like "King so-and-so was the son of King such-and-such. He reigned for X number of years. He died (sometimes in battle). His son was the next king." It's pretty dry stuff.