King of Ireland in joint rule with his brother Fearghus 559-562. These princes were obliged to make war on the people of Leinster (the Southern Ui Niall); fought the memorable battle of Gabhrah-Liffé, where four hundred of the nobility and gentry of that province were slain, together with the greater part of the army. In this reign Dioman Mac Muireadhach, who governed Ulster ten years, was killed by Bachlachuibh. Donal and Fergus both died of "the plague," in one day.