You can find an ancestor yourself, using the books listed below to pursue your lineage:
Douglas Richardson's Royal Ancestry (5 vols.), Plantagenet Ancestry (3 vols.), and Magna Carta Ancestry (4 vols.); Frederick Lewis Weis's Ancestral Roots of Certain American Colonists Who Came to America before 1700 (8th ed.); Gary Boyd Roberts's Royal Descents of 900 Immigrants who came to the American Colonies, Quebec, or the United States (prior versions were 500 Immigrants... and 600 Immigrants...), and George Edward Cocayne's The Complete Peerage, edited by the Hon. Vicary Gibbs.
Head of Brian Boru, Dublin Castle