Background

Gillacommain mac Niall was a member of the SíOl Muiredaig dynasty, who ruled as kings of The Connachta in what is now central County Roscommon

County Roscommon

County Roscommon is a county in Ireland. It is located in the West Region and is also part of the province of Connacht. It is named after the town of Roscommon. Roscommon County Council is the local authority for the county...

. By the mid 10th-century they had expanded south-west into the north-east of County Galway

County Galway

County Galway is a county in Ireland. It is located in the West Region and is also part of the province of Connacht. It is named after the city of Galway. Galway County Council is the local authority for the county. There are several strongly Irish-speaking areas in the west of the county...

. Here a branch of the kindred seized territory and renamed it Uí Díarmata

Uí Díarmata

Uí Díarmata was a local kingdom located in what is now north County Galway.-Origins:The ruling dynasty took its name from King Diarmait Finn of Connacht , and the territory in turn was named after them. It seems to have been created by the Uí Briúin in the ninth century during a wave of expansion...

, after its founder, Diarmada Finn mac Tomaltaig, who was in turn a great-grandsonson of King Indrechtach mac Muiredaig

Indrechtach mac Muiredaig

Indrechtach mac Muiredaig Muillethan was a King of Connacht from the Uí Briúin branch of the Connachta. He was the son of Muiredach Muillethan mac Fergusso , a previous king. He was of the Síl Muiredaig sept of the Uí Briúin....

 (died 723

723

Year 723 was a common year starting on Friday of the Julian calendar. The denomination 723 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.- Religion :* Saint Boniface fells Thor's Oak near...

).

Death and successors

Gillacommain is not known to be attested in the genealogies, nor is there any other reference to him or his father, Niall. He was king in 991

991

Year 991 was a common year starting on Thursday of the Julian calendar.- Europe :* Battle of Maldon: The Anglo-Saxons are defeated by Viking invaders led by Olaf Tryggvason, later Olaf I of Norway....

 but was at war with Cú Ceanain mac Tadhg

Cú Ceanain mac Tadhg

Cú Ceanain mac Tadhg, Prince of Uí Díarmata, ancestor of the Concannon family, died 991-Background:Cú Ceanain mac Tadhg was a member of the Síl Muiredaig dynasty, who ruled as kings of The Connachta in what is now central County Roscommon. By the mid 10th-century they had expanded south-west into...

, a son of his predecessor. They war ended with their mutual deaths, and another unattested member of the Uí Díarmata, Muirgheas mac Aedh, became king. Gillacommain left no known descendants, and after 999

999

Year 999 was a common year starting on Sunday of the Julian calendar.- Europe :* Silesia is incorporated into territory ruled by Boleslaus I of Poland.* The Orsay commune is founded.- Asia :...

, all subsequent Uí Díarmata kings descendended from Cú Ceanain mac Tadhg.