[3] According to local historian Peadar Livingstone, the Mugdorna are described as being a powerful people in the "archaic" period and may have been rulers of Ulster before the ascendancy of the Ulaid.

[3] Francis John Byrne points out that the name Mugdorna, 'the slave folk', denotes their low-caste non-Gael origins and that they are the one people of the Airgíalla for whom no specific ethnic background is supplied.

[4] According to the Dinnsenchus they were named after a shepherd called Boirche who herded on the mountains the cattle of Ross, son of Imchadh, a king of Ulaid in the third century.

According to the Annals of Ulster around 1165 the Uí Echach asked Muircertach Ua Lochlainn, High-King of Ireland, that the kingship of Ulaid be given to Eochaidh Mac Duinn Sleibhe.

[5] In the latter half of the 12th century, a group of the Mugdorna emigrated from Cremorne (from Irish: Crioch Mughdurna) to what is now south County Down where they settled in Bairrche to form a new kingdom.