Fergus Dubdétach ("black-tooth") was, according to medieval Irish legend and historical tradition, a king of the

Ulaid Ulaid (Old Irish, ) or Ulaidh (Modern Irish, ) was a Gaelic over-kingdom in north-eastern Ireland during the Middle Ages made up of a confederation of dynastic groups. Alternative names include Ulidia, which is the Latin form of Ulaid, and in ...

who was briefly High King of Ireland. He took the High Kingship after his predecessor,

Lugaid mac Con Lugaid Mac Con, often known simply as Mac Con, was, according to medieval Irish legend and historical tradition, a High King of Ireland. He belonged to the Corcu Loígde, and thus to the Dáirine. His father was Macnia mac Lugdach, and his moth ...

, was expelled from Tara by

Cormac mac Airt Cormac mac Airt, also known as Cormac ua Cuinn (grandson of Conn) or Cormac Ulfada (long beard), was, according to medieval Irish legend and historical tradition, a High King of Ireland. He is probably the most famous of the ancient High King ...

and killed in Munster by Cormac's poet Ferches mac Commáin. Fergus and his two brothers, Fergus Caisfhiachlach ("rough-tooth") and Fergus Foltlebair ("long-hair"), then expelled Cormac to Connacht and Fergus took the throne. He ruled for a year, before he was defeated by Cormac, with the assistance of Tadg mac Céin and Lugaid Láma, in the Battle of Crinna. The ''

Lebor Gabála Érenn ''Lebor Gabála Érenn'' (literally "The Book of the Taking of Ireland"), known in English as ''The Book of Invasions'', is a collection of poems and prose narratives in the Irish language intended to be a history of Ireland and the Irish fro ...

'' makes no reference to Fergus' descent.

Geoffrey Keating Geoffrey Keating ( ga, Seathrún Céitinn; c. 1569 – c. 1644) was a 17th-century historian. He was born in County Tipperary, Ireland, and is buried in Tubrid Graveyard in the parish of Ballylooby-Duhill. He became an Irish Catholic priest and ...

gives him a long genealogy, naming his father as Finnchad, son of Ogaman, son of the former High King and king of the Ulaid Fíatach Finn. The ''

Annals of the Four Masters The ''Annals of the Kingdom of Ireland'' ( ga, Annála Ríoghachta Éireann) or the ''Annals of the Four Masters'' (''Annála na gCeithre Máistrí'') are chronicles of medieval In the history of Europe, the Middle Ages or mediev ...

'' name Fergus' father as Imchad, but traces his descent no further.''

'
M226
/ref> The ''Lebor Gabála'' synchronises Lugaid's reign with that of the Roman emperor Commodus (180–192). The chronology of Keating's ''Foras Feasa ar Éirinn'' dates his reign to 203–204, that of the ''Annals of the Four Masters'' to 225–226.

References

Legendary High Kings of Ireland {{Ireland-royal-stub