Niall Glúndub mac Áedo (d. October 919) was a 10th century Irish king of the Cenél nEógain and High King of Ireland. While many Irish kin groups were members of the Uí Néill, tracing their descent from Niall of the Nine Hostages (Niall Noígallach), the O'Neill take their name from Niall Glúndub rather than the earlier Niall. His mother was Máel Muire, daughter of Kenneth MacAlpin, King of Scots.

Son of Aed Finliath, Niall is first recorded succeeding his brother Domnall mac Áeda as King of Aileach upon his death in 911. Extending his control to neighboring kingdoms, Niall defeated the Kings of Dál nAraidi and Ulaid at the Battles of Glarryford (in present day County Antrim) and Ballymena before his defeat by high-king Flann Sinna mac Maíl Sechnaill of the Clann Cholmáin Uí Néill at the Battle of Crossakeel (near present day County Meath). Following Flann's death in 916, Niall succeeded him as High King of Ireland. It was during his reign in which he would reestablish the Óenach Tailteann, a traditional gathering of Irish clans.

Opposing the invasion by the Northmen during the next several years, Niall's forces fought a large battle against a group of Northmen in the summer of 917, ending inconclusively. With the support of the clans of Leth Cuinn (Northern half of Ireland), the Uí Néill eventually acknowledged his claim to the throne. Despite his continued offensive against the Northmen however, they would continue to settle the area in large numbers, establishing strongholds in Dublin and various ports on the eastern coast. Continuing to wage war against the Northmen, Niall advanced towards into Leinster, supported by the Uí Néill clans, the Airgíalla and the Ulaid. However, his forces were decimated by the Northmen under Sitric the Blind as Niall was killed, along with twelve other chieftains, at the Battle of Kilmashoge (near Rothfarham) in October. He was succeeded as High King by Donnchad Donn mac Flainn, son of Flann Sinna, and as King of Ailech by his son Muirchertach mac Néill, "the Hector of the Western World".

References

    * Webb, Alfred. A Compendium of Irish Biography: Comprising Sketches of Distinguished Irishmen and of Eminent Persons Connected with Ireland by Office or by Their Writings, New York: Lemma Publishing Corporation, 1970.