Angulo, Gilbert de (d. 1213), lord of Morgallion and Anglo-Norman adventurer, belonged to a family of possible Flemish origin which had adopted its toponymic from Angle, Pembrokeshire, Wales. Gilbert and his brothers Philip and William were sons of Jocelin, baron of Navan, whose personal name was gaelicised, apparently post hoc, as ‘Oisdealb’. The family being vassals of the de Lacy lords of Meath, Gilbert was granted the barony of Morgallion by Hugh de Lacy (qv) but, having taken service with the king of Connacht, Cathal Crobderg Ua Conchobair (qv), he was outlawed (1196), along with his brother Philip, and deprived of his Meath lands. In return for his services, Gilbert was rewarded by Cathal Crobderg with the cantred of Maenmag, around Loughrea, Co. Galway. His brother Philip received lands in the east of Co. Mayo, which were plundered (1225) by a dissident Ua Conchobair dynast, apparently in alliance with Ua Ruairc the king of Bréifne.
Following a campaign on behalf of the king of Connacht against the rulers of the north-west, Gilbert erected a castle (c.1210) at Caol Uisce on the River Erne. He was slain there (1213) by the men of Fermanagh. The descendants of Gilbert and Philip, becoming increasingly gaelicised, adopted the patronymic ‘Mac Oisdeailb’ (Costello). Their lands in Mayo formed the barony of Costello.