Cerball (d. 888), son of Dúngal and king of Osraige, was certainly among the most distinguished representatives of the dynasty of Dál mBirn. As in the case of his nephew Cennétig (qv) son of Gáethíne, the most detailed account of Cerball's career is in the Fragmentary Annals, but he is also adequately documented in the principal annals. His family was a relative newcomer to regional politics; his father, Dúngal son of Fergal, died as king of Osraige in 842. He had at least one brother, Riacán, and a sister Lann. She married Gáethíne king of Loíches and was mother of Cennétig (mentioned above); subsequently, she married the king of Tara, Máel-Sechnaill (qv) son of Máel-ruanaid, for whom she bore a son Flann Sinna (qv), and later still she was the wife of Áed Findliath (qv). Cerball married Máel-Sechnaill's daughter Ailbi, who was the mother of his son Diarmait. He had at least one other son, Cellach.
It appears that Cerball was his father's immediate successor in the kingship. He first enters the historical record against the background of the intensified viking raids that characterised the second third of the ninth century. For some fifteen years he vigorously opposed Norse designs in the Barrow valley. In 847 he besieged a viking warband for two weeks, and the following year routed a force led by Haakon from the longphort of Dublin, slaying 200 of their number. For the 850s, the Fragmentary Annals supply a veritable catalogue of victories by Cerball over the Norsemen, achieved in more than one instance by exploiting divisions among the foreigners. In 851 he recruited the assistance of Horm (Ormr), a Danish warlord, to defeat a Norwegian force at Cruachu in the land of the Éoganachta (near Kilenaule, Co. Tipperary). Apparently, he retained some of Horm's troops in his service after the latter's departure from Ireland. In 855 Cerball defeated the warlord Rothlaib (Hró∂úlfr) in the battle of Ath Muiceda; some years later, with the assistance of his nephew Cennétig, he sacked the longphort of Rothlaib. Between 858 and 863 he defeated viking forces on land in Araide Tíre (barony of Owney and Arra, Co. Tipperary), at Achad mic Erlaige (seemingly near Kilkenny city), at Sliab Mairge (barony of Slievemargy, Co. Laois), and at Fertae Cairech (Fertagh, near Johnstown, Co. Kilkenny).
By 858, however, he had come into conflict with Máel-Sechnaill, king of Tara. It seems that the two were brothers-in-law by the early 850s; the Fragmentary Annals (§246) claim that Cerball took the hostages of Munster on behalf of Máel-Sechnaill in 854. Relationships between the two deteriorated, less because of Cerball's effective handling of the Norsemen during this period than because of his pursuit of ambition in Leinster. In 858 he crossed into Leinster and took hostages from the dynasty of Uí Muiredaig. In response, his own kingdom was invaded by Máel-Sechnaill, and he was defeated at Carn Lugdach. The often partisan Annals of Inisfallen assert that the territory of the Southern Uí Néill was plundered by the men of Osraige the following year, but this is unsupported by other sources. In 859, however, Cerball did resolve his differences with Máel-Sechnaill at the rígdál (royal meeting) of Ráith Áeda maic Bricc (Rahugh, Co. Westmeath), where he made formal submission. Perhaps his marriage to Máel-Sechnaill's daughter Ailbi resulted from this renewed alliance. It further seems reasonable that the agreement of Ráith Áeda enabled Cerball, in 861, to celebrate with impunity the Óenach Raigne (fair of Raigne, on the plain between Slievardagh and Slievenamon), traditionally a prerogative of the Éoganacht king of Cashel; the king of Tara was less concerned about Osraige expansionism in east Munster.
After 862, Cerball was allowed a more free rein by Máel-Sechnaill's successor in the kingship of Tara, Áed Finnliath of the Cenél nÉogain. He turned his attentions to Leinster, the ruling dynasties of which had been seriously weakened by the establishment of Norse colonies. An early venture against the Leinstermen in 864 seriously backfired when Osraige forces were pursued back across their own territory and into Munster, where they were decimated by the Éoganachta. Cerball subsequently wreaked revenge on the Munstermen. He struck at Leinster again in 868, but without a decisive result. Then, two years later, with his nephew Cennétig and with support from Áed Finnliath, he invaded northern Leinster and inflicted a signal defeat on the Uí Dúnlainge king, Muiredach son of Bran (qv) (d. 838), at Dún Bolg. With the potential for regional opposition thus reduced, Cerball may well have built on his connections with the Norsemen of Dublin; according to later traditions, several members of his family married into the Norse nobility. Certainly, early Icelandic pedigrees in ‘Landnámabók’ accord considerable prominence to ‘Kjarvall Írakonungr’, often identified with the powerful king of Osraige.
Cerball's family is accorded a prominent role in the settlement of Iceland. He also features in medieval Norse literature; an episode in ‘Gretti's saga’ has him campaigning on the Hebridean island of Barra. The precise historical basis for much of this is difficult to ascertain; some Icelandic connections and, even more so, hints concerning a ‘protectorate’ over Dublin, perhaps relate to the achievements of Cerball's descendants, specifically Donnchad (qv) son of Gilla-Pátraic, who laid claim to overkingship of Leinster in 1033. Cerball himself died in 888, and was apparently buried at Saigir Ciaráin (Seirkieran), one of the principal ecclesiastical foundations of Osraige. A flat burial stone from that site, which carried the simple inscription ‘ór[oit] do Cerball’ (pray for Cerball), is believed to have been his. His immediate successor in the kingship was his brother Riaccán (d. 894). Cerball's son Diarmait (d. 928), whose reign was interrupted by his brother Cellach (d. 908), became king in 894. Ironically, most of the later rulers of Osraige descended from Cellach.