Lethlobar (d. 873), son of Loingsech and overking of Ulaid, belonged to the dynasty of Dál nAraide. His grandfather, Tommaltach son of Indrechtach, had briefly held the dignity of overking of Ulaid before his death (790). His father, Loingsech, however, does not seem to have achieved any great distinction; Lethlobar's immediate predecessor as king of Dál nAraide was a distant kinsman, Eochaid son of Bressal, who was slain in an internecine conflict.
Before 828 Lethlobar had achieved the kingship of Dál nAraide, the territory of which straddled the present counties Antrim and Down. That year, he inflicted a severe defeat on the vikings who were then harrassing the east coast. It appears that over the following twenty years or so Lethlobar gradually rebuilt the fortunes of his dynasty. In 855 he repulsed an incursion into Dál nAraide by Áed Findliath (qv), Cenél nÉogain king of the Northern Uí Néill. Perhaps this victory strengthened Lethlobar's position as a candidate for the overkingship of Ulaid, which for more than half a century had rested with the rival dynasty of Dál Fiatach. Certainly, when his Dál Fiatach rival Matudán son of Muiredach died on pilgrimage in 857, Lethlobar succeeded to the provincial dignity. For the remainder of his reign, it seems that Lethlobar ruled his enlarged realm in peace without any further threat from the Northern Uí Néill.
In 873, aged probably close to 70, Lethlobar died from a wound to the stomach in unknown circumstances. He was immediately succeeded as king of Dál nAraide by his son Cennétig (d. 900). The provincial overkingship reverted to Dál Fiatach and was taken by six kinsmen of Matudán in succession. These dynasts, however, had short reigns; at least two were slain in internal conflicts, and the last two were so ineffective that Cennétig was able to advance his claim to the overkingship. The later kings of Dál nAraide descended from Lethlobar through his son Cennétig and grandson Loingsech (d. 932); taking the surname Ua Loingsich, they maintained their kingship till the coming of the Anglo-Normans in the twelfth century.