The Genealogy of the kings of Ulster
The images below of the kings of Ulaid (Ulster) are taken from the book:
Irish Kings and High-Kings. 3rd revised edition, Dublin: Four Courts Press, 2001 by Francis J. Byrne. It is considered the best source for information about ancient Irish kings.
The images to the right are about the same material, but taken from a book by William Reeves, who specializes in the history of County Down which is where the Dál Fiatach lived. More information and the full section on the Ulaid kings is found here.
The first king in these list to use the surname O'Heochaidh is number 56 in Reeves who was Donnsleibhe O'Heochaidh or Dunlevy O'Heoy (Hoy). He took his surname from his great grandfather Eochiadh (Owey) who was king number 44 and was killed by the O'Neills in 1004.
Some of the last kings in these lists took a new surname after Donnsleibhe O'Heochaidh and were called MacDunlevy.