Crimthann mac Fidaig

Crimthann Mór, son of Fidach /ˈkriːvən ˈmɔər mæk ˈfiːaɪ/, also written Crimthand Mór, was a semi-mythological king of Munster and High King of Ireland of the 4th century. He gained territory in Britain and Gaul, but died poisoned by his sister Mongfind. It is possible that he was also recognised as king of Scotland or Alba. As his Gaelic name means fox, Crimthand Mór mac Fidaig becomes Great Fox, son of Woodsman (Fidach) in English. This Crimthann is to be distinguished from two previous High Kings of Ireland of the same name, two Kings of Leinster, and another King of Munster, among others. Importantly, he is included in the Baile Chuinn Chétchathaig (summary), and is thus the last High King of Ireland from Munster until Brian Bóruma, over six hundred years later.

In addition to having his reign described by Geoffrey Keating and mentioned in the Annals of the Four Masters, Crimthand Mór mac Fidaig also plays a major role in many stories belonging to the Cycles of the Kings. In these he is typically succeeded by Niall of the Nine Hostages as High King of Ireland and by Conall Corc as King of Munster, while his sister Mongfind, the first wife of Eochaid Mugmedón, becomes the ancestor of the Three Connachta. Thus this otherwise obscure kindred is central in the mythologies of most of the great medieval Irish dynasties.

...
Wikipedia