Fergal (d. 966), grandson of Ruarc, son of Art and overking of Connacht, belonged to the dynasty of Uí Briúin Bréifne. His grandfather Ruarc (d. 898) and great-uncle Flann (sl. 910), both sons of Tigernán, in turn ruled the Connacht–Ulster border kingdom of Bréifne; but it is not clear if his father Art reigned as king. His immediate predecessor was probably his cousin Áed son of Tigernán son of Ruarc, slain in a conflict with the Airgialla (947). Fergal made a calculated political alliance when he married Bébinn, daughter of Tadc son of Cathal, overking of Connacht, whose Uí Briúin Aí dynasty had traditionally monopolised that dignity. Bébinn had previously been married to Domnall, whose father Congalach Cnogba (qv) son of Máel-mithig was king of Tara. It is not stated that she was the mother of Fergal's son Áed.
It seems clear that Fergal had secured the kingship of Bréifne by mid-century, and was already involved in extending his lordship in the direction of Connacht. In 954 he led a successful invasion of two sub-kingdoms of Mide, Tethbae and Cairpre (Co. Longford), and killed the ruler of the latter. His activities had already attracted the attention of the powerful Uí Néill king, Domnall Ua Néill (qv), who made an expedition to Bréifne in 955 and took hostages. The following year, on the death of his father-in-law Tadc son of Cathal, Fergal capitalised on the temporary weakness of Uí Briúin Aí and, presumably by using his wife's connections, made good his claim to overkingship of Connacht. According to the regnal lists, he retained that dignity for ten years. Ultimately, however, he failed to withstand pressure from the Uí Néill rulers. In 965 he was forced to yield hostages to Domnall Ua Néill, by this time king of Tara, who plundered Connacht.
A year later Fergal was slain in battle by his wife's former husband, Domnall son of Congalach, now king of Brega. His dynasty continued to pursue pretensions in Connacht; his immediate successor, Ualgarg grandson of Ruarc (a brother or a cousin) was killed in 970 by his brother-in-law, Conchobar (qv) son of Tadc, who now laid claim to the provincial kingship. Fergal's son Áed, king of Bréifne, was slain in 1015 by the Uí Briúin Aí overking, Tadc in Eich Gil Ua Conchobair (qv). Three of his descendants later claimed overkingship of Connacht, including his grandson Art Uallach (d. 1046), great-grandson Áed Ua Ruairc (qv) (d. 1087), and four-times-great-grandson Domnall (d. 1102). The last-mentioned was first cousin once removed of Tigernán Ua Ruairc (qv).