Máel mac Donngaile (died 859), known as Máel Gualae, was a King of Munster from the Eóganacht Chaisil branch of the Eoganachta, the ruling dynasty of Munster. He was of the Clann Faílbe sept of this branch and a grandson of Tnúthgal mac Donngaile (died 820), whom some sources name as King of Munster and brother of Áilgenán mac Donngaile (died 853), also King of Munster. His branch of the ruling dynasty had their lands in the Cashel area of modern County Tipperary. He reigned from 856 to 859. After the death of Áilgenán in 853 there was an interregnum until the succession of his brother Máel Gualae in 856.<ref>Annals of Innisfallen, AI 856.1</ref> The Danes had arrived in Ireland in 849 and took control of Dublin in 851. The dispersed Norse went off to plunder different areas of Ireland and a rivalry began between these two Viking groups with Irish kings using this rivalry in their own conflicts. A number of men in Munster joined up with these Norse and were known as Gall Gaedil ("foreign Gaels"). Cerball mac Dúnlainge (died 888), King of Osraige aligned himself with the Danes versus the Norse to become the most powerful ruler in southern Ireland during this period. During the interregnum, the High King of Ireland Máel Sechnaill mac Máele Ruanaid (died 862) of Clann Cholmáin led an expedition into Munster in 854 as far as the borders of the Déisi in Tipperary County and took hostages from Munster. The Fragmentary Annals of Ireland claim that Cerball, brother-in-law of the high king, was sent by the high king into Munster as well to claim the hostages. According to the Annals of the Four Masters, the Norse had instigated the opposition to the high king in Munster. The high king appeared again at Cashel to take hostages from Munster in 856, probably at the time of the accession of Máel Gualae. The Norse activities in Munster were a disruptive influence and around 855 the men of Munster appealed to Cerball of Osraige for aid against the Norse. Cerball arrived with a force of Danes under a leader named Horm and they surrounded the Norse and massacred them. In 856 a Norse force slew Gormán son of Lonán, heir designate of Cashel, at Loch Cenn. In 857 Cerball and his Danish allies, Amlaíb Conung and Ímar, won a victory over the Norse and Gall