LETHLOBOR (d. 871), Irish king, son of Longsech, first appears in history as victor in battle against the Danes in co. Down in 826. He was then a king of Dal Araidhe, a territory including the southern half of Antrim and the greater part of Down. His rule only extended over the southern half. In 853 he repulsed an invasion of Aodh MacNeill, and during his long life this was the only serious attack made by the greater Ulster upon the lesser. He became king of all lesser Ulster, or Ulidia, and died of a wound 'after a good life' (Ann. R. Eireann, i. 516), in 871. Ulidia was perhaps more subject to attack from without by the Danes, and from the land side by the increasingly powerful Cinel Eoghain and Oirghialla, than any other, and it is clear that Lethlobor was one of the most powerful of the kings of Ulidia. He was succeeded immediately by his son Cennetich as king of Dal Araidhe, and, after an interval, as king of Ulidia.
[Book of Leinster, MS. of the twelfth century, facs. fol. 41, cols. 3 and 5; Annals of Ulster, ed. Hennessy, i. 325, &c.; Annala Rioghachta Eireann, ed. Donovan, i. 516, &c.]