Ua hAingliu, Samuel (d. 1121), fourth bishop of Dublin, was nephew of his predecessor Donngus Ua hAingliu (qv), who died of plague in 1095. He had been trained as a Benedictine monk at St Albans in England. He was consecrated bishop of Dublin by Anselm, archbishop of Canterbury, in Winchester cathedral on 27 April 1096. Apparently, the consecration took place only after some delay caused by a doubt in Anselm's mind about the suitability of the candidate. Samuel may have considered himself a suffragan of Canterbury, but the wording of his formal vow of obedience to Anselm, ‘archbishop of the holy church of Canterbury and primate of all Britain’, leaves the matter unclear.
When Samuel was returning to Ireland, Anselm entrusted him with a letter for Muirchertach Ua Briain (qv), requesting him to hold a synod ‘of the good and wise men of your kingdom’ to endeavour to correct some of the abuses in the Irish church and society, including clerical marriage and canonically incestuous marriages between lay people. Later that year, Muirchertach held a synod, most likely at Waterford, for the purpose of establishing a new diocese in that Norse-Irish city. In a subsequent letter from the people and clergy of Waterford to Anselm requesting the appointment of Máel-Ísu Ua hAinmire (qv), a Benedictine monk and priest of Winchester, as first bishop to the new see, Samuel's name appears among the signatories after that of Máel-Muire Ua Dúnáin (qv), bishop of Meath.
In the following year, Samuel received an indignant letter from Anselm, complaining that he had allegedly been handing out some of the property, books, vestments, and altar-plate belonging to the canons of Christ Church cathedral; that he had driven out the monks from the same church; and that he was insisting on having his ceremonial episcopal cross carried before him in solemn procession in the manner of an archbishop. The letter had been sent to Bishop Máel-Ísu, then in Waterford, with a terse covering letter, stating: ‘And since I can find no person more suitable than you through whom I can send him my letter, I beg you . . . to hand it to him in person, and to warn him . . . to pay heed to the admonition which I am sending him in writing.’ Samuel, it has been plausibly suggested, had recently established the church known as St Michan's (now the oldest parish church in Dublin), wishing perhaps to establish it as Dublin's cathedral in place of Christ Church. That may explain why he allegedly removed some Christ Church property, that had been presented by Anselm's predecessor Lanfranc in 1085, and given it to St Michan's; in addition, he was said to have evicted some of the monks from Christ Church following a quarrel. It has been suggested that the episcopal effigy in St Michan's is that of Samuel.
Apart from his attendance at the synod aimed at establishing a diocese of Waterford, Samuel seems to have distanced himself from the reform movement then taking place in the Irish church. The diocese of Dublin is not included among those established at the synod of Ráith Bressail (1111). Samuel's ambiguous attitude towards reform might explain the seizure by Cellach (qv) of the bishopric of Dublin after his death in 1121 and Cellach's opposition to his chosen successor Gregory (qv).