Fergal (d. 722), son of Máel-dúin and king of Tara, belonged to the Uí Néill dynasty of Cenél nÉogain. His father Máel-dúin died as king of his line in 681; his mother was Cacht daughter of Cellach (qv) son of Máel-Cobo of Cenél Conaill. Fergal himself maintained the alliance with his western neighbours, marrying the daughter of a certain Ernán; she was the mother of his son Áed Allán (qv), although a late and colourful tale in the Fragmentary Annals (§177) makes Áed the illegitimate son of Fergal and a nun, a daughter of Congal Cennmagair (qv) of Cenél Conaill, king of Tara. A later wife, Aithechda daughter of Cian (who probably belonged to the Cianachta), was the mother of Niall Frossach (qv). Fergal had two other sons, Conchobar and Colcu.
Already a prominent dynast of Cenél nÉogain (even if the styling rígdamna Éireann – eligible for the high-kingship of Ireland – in the Fragmentary Annals (§177) is viewed as anachronistic), Fergal gained notice in 707 when, in alliance with the ruler of Cenél Cairpri, he slew Indrechtach, overking of Connacht. He emerged as the leading contender for the kingship of Tara following the death of Congal Cennmagair in 710. Middle Irish king-lists give different accounts of the length of Fergal's reign as king of Tara – the list in Rawlinson B. 502 gives him ten years – but there is a strong case for identifying him in the Old Irish regnal poem of Tara, ‘Baile Chuinn’, where he is probably represented in the kenning ‘In Cailech’ (the cock).
Fergal certainly strove – with a considerable degree of success – to extend the influence of his dynasty. Building on foundations laid by his predecessors, he furthered Uí Néill expansion eastwards into mid-Ulster, defeating the Airgialla in the battle of Sliab Fuait (in the Fews, Co. Armagh) in 711. Having subjugated the Airgialla dynasties, he increasingly depended on them for military support. He also asserted his authority over the midland Uí Néill dynasties, and seemingly promoted the Clann Cholmáin dynast Murchad Midi (qv), son of Diarmait, to a kingship of the Uí Néill under his suzerainty. In 714 he expelled the latter's rival, the Síl nÁedo Sláine dynast Fógartach (qv) son of Niall, and four years later slew Fógartach's brother Conall Grant.
Fergal also sought to dominate the Laigin, or Leinstermen; in 719 he defeated their overking Murchad (qv) son of Bran Mút at Fennor and slew Áed son of Cellach Cualann (qv). Two years later he laid waste the plain of Leinster. The Leinstermen retaliated, seemingly in alliance with Cathal (qv) son of Finguine and overking of Munster, and devastated the plain of Brega, but Fergal managed to reassert his overlordship of Leinster and took hostages. Then, perhaps because no tribute was forthcoming, in 722 he invaded Leinster in force. He was defeated and slain in the disastrous battle of Allen, as related in the tale ‘Cath Almaine’. His immediate successor as ruler of Cenél nÉogain was his son Áed Allán, who eventually gained the kingship of Tara.