Dui Dallta Dedad ("foster-son of
Deda mac Sin"), son of Cairpre Lusc, son of
Lugaid Luaigne, was, according to medieval Irish legend and historical tradition, a
High King of Ireland. He took power after killing his predecessor, and his grandfather's killer,
Congal Cláiringnech, and ruled for ten years, at the end of which he was killed by
Fachtna Fáthach in the battle of Árd Brestine. The
Lebor Gabála Érenn synchronises his reign with that of
Ptolemy XII Auletes (80–51 BC) in
Egypt and the
civil war between
Pompey and
Caesar in
Rome (49 BC). The chronology of
Geoffrey Keating's
Foras Feasa ar Éirinn dates his reign to 120–110 BC, that of the
Annals of the Four Masters to 169–159 BC.