Gilbert, Claudius (1669/70–1743), clergyman and university benefactor, was born in Belfast, the only son and heir of Claudius Gilbert (qv), a nonconformist clergyman and prolific pamphleteer who appears to have conformed to the established church shortly after 1660, and his wife Margaret. He was educated by Mr Gordon in Belfast before entering TCD as a pensioner on 23 March 1685/6, aged 16. As an undergraduate his principal tutor was probably Dive Downes (1653–1709), later bishop of Cork. He graduated BA (1691) and MA (1693); the degrees of BD, DD, and LLD followed in 1706. He was elected FTCD (1693), Donegal lecturer (1696), and professor of divinity (1722). From 1717 to 1735 he served as vice-provost of the college before becoming rector of Ardstraw in the diocese of Derry from 1735 until his death.
Gilbert was one of the few fellows of TCD in the first quarter of the eighteenth century who was praised for wide-ranging scholarly interests and industry. He was an indefatigable and discerning book collector. The surviving catalogue of books that he compiled shows that he scoured the book dealers and auction houses all over Europe and was probably in touch with other notable Irish bibliophiles such as Edward Worth (qv). Though he acquired some rare first editions and valuable bindings, the strength of his collection was in the number of collected editions and erudite compilations. In range and quality his collection of about 13,000 volumes ranked as one of the finest working libraries in Ireland during the early eighteenth century. The source of Gilbert's income, that was needed to purchase this collection, is unclear.
In 1716, when the provostship was vacant, Archbishop William King (qv) felt that only Richard Baldwin (qv) and Claudius Gilbert were suitable candidates, the former being more senior and the latter more active. As vice-provost Gilbert was left in charge of the day-to-day running of the college, including the management of the college estates and the accounts. Indeed, it was probably this administrative burden that led him, like previous and subsequent vice-provosts, to resign his fellowship and spend the last years of his life as a rector of a parish that was in the gift of the college. Before he retired in 1735 he presented his books and his collection of medals, coins, and mathematical instruments, valued at £12,000, to the college. The Long Room was opened shortly before this date and his library is still shelved in its original order. Before his death Gilbert ensured that the library was properly regulated and he helped to frame the library statutes. In his will he left the college £550 for a lending library, £500 to purchase ‘busts of men eminent for learning to adorn the library’, £800 to purchase advowsons, £500 to help build a steeple above the dining hall, £50 for altar plate, and £50 for needy students. In addition he left £700 to the board of first fruits to purchase land for the building of a parish church in Belfast, £50 for altar plate, and £30 for the poor of the parish of Ardstraw.
He died on 13 September 1743. In accordance with Gilbert's wishes the Flemish sculptor Peter Scheemakers had by 1749 executed 14 marble busts, and these became the nucleus of the college's large collection of busts. In 1758 Simon Vierpyl (qv) was commissioned to make a bust of Gilbert (this now stands alongside the others in the Long Room), and in 1777 the college bursar's accounts show that Thomas Kingsbury was paid £22. 5s. 0d. to paint a portrait (now missing) of Gilbert. His library catalogue and some fragmentary miscellaneous accounts relating to his administration of the college are held in TCD department of manuscripts.