Áed Rúad, Díthorba, and Cimbáeth
Áed Rúad, son of Badarn, Díthorba, son of Deman, and Cimbáeth, son of Fintan, three grandsons of Airgetmar, were, according to medieval Irish legend and historical tradition, High Kings of Ireland who ruled in rotation, seven years at a time. They each ruled for three seven-year stints.
Source: Wikipedia — Áed Rúad, Díthorba, and Cimbáeth (CC BY-SA 4.0)