Clayton, Robert (1695–1758), Church of Ireland bishop of Clogher, antiquary, and religious controversialist, was born in England, possibly at Fulwood, near Preston, Lancashire, the eldest of eight children and first of four sons of John Clayton (1657–1725) and his wife, Eleanor (née Atherton). John Clayton moved to Ireland as prebendary of St Michan's, Dublin (1698–1725), and was later dean of Kildare (1708–25). Robert Clayton was educated either at Westminster School or in Ireland or (probably) both. He entered TCD on 25 June 1710 aged fifteen, graduated BA and was elected fellow in the same year (1714); he later proceeded to MA (1717), LLB (1718), LLD (1722), a senior fellowship (1724–8), and DD (1730). On his father's death he inherited his estate and so could afford to resign his fellowship and marry, which he did on the same day (17 June 1728); his wife was Catherine Donnellan (1703?–1766), a daughter of Nehemiah Donnellan (qv), chief baron of the Irish exchequer until his death (1705).
In London, where he was living in 1729, Clayton came under the influence of the Rev. Samuel Clarke of St James's, Westminster, whose religious views tended to Arianism or even unitarianism. Both belonged to the religious circle of Mrs Charlotte Clayton (Lady Sundon from 1735), a connection of Robert Clayton. She had great influence over the queen consort of George II, Caroline of Brandenburg-Anspach, who also was a disciple of Clarke. The royal connection brought Clayton the see of Killala and Achonry, for which he was consecrated bishop on 10 May 1730. He must have been ordained on becoming a fellow of TCD, though nothing has been ascertained of any pastoral experience and he seems to have visited his Killala diocese only once (May 1732). He was translated to Cork (December 1735), and thence to Clogher (August 1745), the latter a very lucrative see. He inherited estates in England, had a fine house built in Dublin on the south side of St Stephen's Green, designed in Italian style by Richard Castle (qv) in the mid 1730s (latterly called Iveagh House), acquired a country house in Co. Kildare, St Wolstan's near Celbridge (1752), and spent freely.
Clayton had intellectual interests that brought him fellowship of the Royal Society (1746) and the Society of Antiquaries. Soon after their marriage he and his wife visited the continent. In 1737 the 5th earl of Cork and Orrery (qv), writing from Cork, observed that Clayton had ‘brought home with him, to the amazement of our merchant fraternity, the arts and sciences that are the ornaments of Italy’, including pictures by Carlo and Morat and music by Corelli (Orrery papers, i, 206–7). A friend of Richard Pococke (qv), Clayton was a connoisseur of Egyptian remains, and published, as A journal from Grand Cairo to Mount Sinai (1753), what appears to be a translation of an account of a visit made by another person in 1722, with annotations by Clayton on hieroglyphics and mythology. The book was translated into German (1754) and French (1759). Whether Clayton himself visited Egypt is unclear. Clayton's religious beliefs were increasingly unorthodox. Apart from his Arian tendencies, he showed an interest in millenarianism in his first (belated) scholarly work, The chronology of the Hebrew Bible vindicated (1747). This was followed by A dissertation on prophecy (1749), An inquiry into the time of the coming of the Messiah and the restoration of the Jews (1751), and A vindication of the histories of the Old and New Testaments (pts I–II, 1752–4). He predicted among other things the fall of the papacy c.2000.
An anonymous pamphlet, An essay on spirit wherein the doctrine of the Trinity is considered (1750), was undoubtedly by Clayton and is the work on which his fame rests. It pleads in its dedication for religious toleration of dissenters, Jews, quakers, and even catholics, and then sets out the writer's Arianism and develops a metaphysical theory of spirits. The theory was used by Charles Johnstone (qv) for his novel Chrysal (1760–65). Clayton's tolerance of catholics was qualified, for he voted for the bill providing for the registration of catholic priests (October 1751). Clayton's heterodoxy was tolerated for a while but spoilt his prospects of appointment to the archbishopric of Tuam (1751) and eventually, after he proposed in the Irish house of lords the removal of the Nicene and Athanasian creeds from the prayer book (2 February 1756) and brought out a third part of his Vindication (1757), he was summoned for trial on a charge of heresy before an ecclesiastical commission. Before it began he died of a fever, on 26 February 1758, aged sixty-four, at his Dublin house and was buried at Donnybrook. Several of his sermons were published. To his wife, who was childless, he left £1,800 p.a. and a vast fortune. His landed property he left to a kinsman, a Lancashire lawyer, Richard Clayton (1702–70), who later was justice of the common pleas in Ireland (1765–70). A portrait of Bishop Clayton and his wife by James Latham (qv) is in the National Gallery of Ireland. A bust is in the library of TCD.