Colla , a pseudo-historical ancestor-figure of the Airgialla, is triplicated as Colla Fo-Chríth, Colla Mend, and Colla Uais, who are represented in genealogical tradition as the respective ancestors of the ruling dynasties of Airthir and Uí Chremthainn, of the Mugdorna, and of Uí Meic Uais. The brothers Colla were allegedly great-grandsons of Cormac (qv) son of Art, and so cousins of Muiredach Tírech, king of Tara. According to the origin-tale of the Airgialla (which was probably established by the eighth century), the brothers slew their uncle, the father of Muiredach Tírech, and spent time in exile in Scotland for the crime of fingal, kin-slaying. On their return, they were permitted to make sword-land of mid-Ulster, which thus came under the overlordship of the Uí Néill kings, but they themselves were excluded from the privilege of overkingship because of their kin-slaying.
Essentially, the story of the brothers Colla is a device to explain how the Uí Néill rulers subjugated the original dynasties of mid-Ulster, which historically did not take place earlier than the seventh century, and so prevented the development of a strong rival kingship in the region. The role of the Collas in genealogical tradition and in the Airgialla origin-tale has been amply discussed by scholars of Old Irish literature.