Ua hAinmire, Máel-Ísu (Malchus) (c.1047–1135), first bishop of Waterford, was one of the earliest and most important figures in the eleventh-century reform movement in the Irish church. Nothing is known of his ancestry or family background. In 1095 Muirchertach Ua Briain (qv), king of Munster, held a synod at Waterford with the purpose of establishing a new diocese in that Norse-Irish city. Following the synod, the people and clergy of Waterford wrote to Anselm, archbishop of Canterbury, asking him to accept the candidate they had chosen for bishop: ‘This priest Malchus. . . who is well known to us as of noble birth and character, steeped in apostolic and ecclesiastical learning, catholic in his faith’ (letter reproduced in Eadmer's ‘Historia novorum’). The letter was signed by Muirchertach Ua Briain; Domnall Ua hÉnna (qv), bishop of Killaloe and Muirchertach's chief bishop; Samuel Ua hAingliu (qv), bishop of Dublin; and other notable Irish prelates.
Máel-Ísu was subsequently consecrated bishop by Anselm and two assistant bishops in Canterbury on 28 December 1096. He had previously lived as a Benedictine monk and priest under Bishop Walchelin at Winchester, where he took the latinised form of his name, ‘Malchus’, by which he is known in ecclesiastical documents. His choice as candidate was supported by Bishop Walchelin in a letter which he wrote to Anselm (Epistulae 202). Máel-Ísu's oath of obedience to Anselm, addressing him as ‘primate of all Britain’, survives in a scroll in Canterbury cathedral. He travelled to Ireland shortly afterwards, most likely bearing with him a letter from Anselm to Muirchertach, which complained in forceful language of the persistence of abuses among the Irish people and clergy. Its description of the abuses in episcopal ordination and other matters are so clearly laid out that it can be surmised that Anselm's detailed knowledge most probably came from Máel-Ísu himself.
An interesting incident involving Canterbury and Dublin shows that Máel-Ísu must already have been one of the most important of the reformed churchmen in Ireland. In 1097 Samuel, bishop of Dublin, received an indignant letter from Anselm, complaining that he had been handing out some of the property belonging to the canons of Christ Church cathedral; that he had driven out the monks from the same church; and was insisting on having his ceremonial episcopal cross carried before him in the manner of an archbishop. This letter was delivered by Máel-Ísu, with a covering letter from Anselm stating that he had appointed Máel-Ísu to admonish Samuel, asserting ‘I can find no person more suitable than you through whom I can send him my letter.’
Máel-Ísu had close connections with the Meic Carthaig dynasty of Munster, and was conferred with the archbishopric of Cashel at the synod of Ráith Bressail (1111). He evidently did not remain in the post for long, returning sometime later to his episcopal seat at Lismore; the death of his successor in the see of Cashel, Máel-Ísu Ua Foglada, is recorded in 1131. Bishop Malachy (qv) of Armagh came south to Lismore in 1121 and placed himself under Máel-Ísu, remaining there till his consecration as bishop of Connor in 1124. Malachy's mentor and predecessor in the see of Armagh, Cellach (qv), was subsequently buried at Lismore in 1129. Lismore was evidently regarded as the centre and source of the Irish reform movement. It was there that Cormac Mac Carthaig (qv), king of Desmond, sought refuge and a monastic retirement under Máel-Ísu following expulsion from his kingdom in 1127. Malachy returned to Lismore after the destruction of his monastery at Bangor in the same year. In 1132, three years after the death of Cellach, Máel-Ísu and Gilbert (qv), bishop of Limerick, called together the bishops and princes to prevail on Malachy to take the see of Armagh from its lay incumbent, Niall (qv) (d. 1139), brother of Cellach, by force if necessary.
Máel-Ísu died at Lismore in 1135 as ‘chief senior of Ireland . . . in the 88th year of his age’ (AFM). His obit in the annals refers to him as ‘bishop of Port Láirge’ (Waterford). He is also commemorated on 11 April in the necrology of the Irish Schottenklöster, which indicates a close connection with the Irish monastic community in Germany. Malachy of Armagh clearly held him in high regard and gave his friend Bernard of Clairvaux some information concerning him, which later featured in Bernard's Life of Malachy.