Cathal mac Ógán is an ancestor of the Ó Cathail–Cahill

Cahill

Cahill is a name of Irish origin. In Irish, It is the anglicized version of the Gaelic "Ó Cathail" meaning "descendant of Cathal." "Cathal" consists of two parts: "cath" means battle; the second could be "val" , so that the name as a whole meant "battle ruler" or "strong in battle", or it could...

 family 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...

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Cathal was a member of the Uí Fiachrach Aidhne

Uí Fiachrach Aidhne

Uí Fhiachrach Aidhne was a kingdom located in what is now the south of Co. Galway.-Legendary origins and geography:...

, and a thirteen-time great-grandson of Nath Í

Nath Í

Nath Í, an early Irish personal name for males, may refer to:*Nath Í mac Fiachrach, 5th-century legendary king of Connacht*Nath Í of Cúl Fothirbe, saint of the Dál Messin Corb of Leinster...

, King of Connacht. His grandchildren and great-grandchildren were the first to bear the surname Ó Cathail (i.e., ua Cathal, grandson/descendant of Cathal) and till the 13th century would contest the kingship of Aidhne

Aidhne

Aidhne also known as, Uí Fhiachrach Aidhne, Maigh Aidhne / Maigh nAidhne was the territory of the Ui Fiachrach Aidhne, a tuath located in the south of what is now County Galway in the south of Connacht, Ireland. Aidhne is coextensive with the present diocese of Kilmacduagh...

 with the descendants of Seachnasach mac Donnchadh

Seachnasach mac Donnchadh

Seachnasach mac Donnchadh, ancestor to the family of O'Shaughnessy, fl. 10th century.Seachnasach was a member of the Uí Fiachrach Aidhne dynasty, formerly Kings of Connacht. By the tenth century their power had been reduced to Aidhne, a small kingdom in what is now south County Galway...

, Scannlán mac Fearghal

Scannlán mac Fearghal

Scannlán mac Fearghal, ancestor of the Ó Scannláin family of County Galway, fl. 10th century.Scannlán was a member of the Uí Fiachrach Aidhne dynasty of south County Galway, and is listed in the genealogies as a seventeen-times great-grandson of King Guaire Aidne mac Colmáin of Connacht, who died...

, Eidhean mac Cléireach

Eidhean mac Cléireach

Eidhean mac Cléireach, ancestor of the Ó hEidhin/Hynes family of County Galway, fl. 800.Eidhean was a member of the dynasty of Uí Fiachrach Aidhne, and a descendant of Guaire Aidne mac Colmáin , Fiachrae mac Eochaid Mugmedon and thus distantly related to the dynasty of Uí Néill...

 and Giolla Ceallaigh mac Comhaltan

Giolla Ceallaigh mac Comhaltan

Giolla Ceallaigh mac Comhaltan, fl. 10th century, ancestry to the MacGiolla Ceallaigh .Giolla Cellaigh - devotee of Saint Ceallaigh - was a member of the Uí Fiachrach Aidhne of south Galway, and was a six-time great-grandson of Guaire Aidne mac Colmáin, King of Connacht...

. While the family did provide a number of rulers of the area, ultimately Cathal's descendants were overthrown and suppressed by the descendants of Seachnasach mac Donnchadh, and remained a minor family till the end of Gaelic Ireland

Gaelic Ireland

Gaelic Ireland is the name given to the period when a Gaelic political order existed in Ireland. The order continued to exist after the arrival of the Anglo-Normans until about 1607 AD...

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Cahill is the name of a number of distinct families in Ireland, and not all are related.