Gahagan, Usher (d. 1749), classical scholar and criminal, was perhaps from Co. Westmeath and may have been educated at TCD, though he did not take a degree. He converted to catholicism, much to the consternation of his family, who henceforth ceased to offer him financial support. Unable to practice at the Irish bar, he married an heiress, whom he had presumed carried with her a considerable fortune. However, owing to his mistreatment of her she returned to her family. Proceeding to London, he edited eleven editions of the classics (1744–9) for the London printer James Brindley's series of Latin classics, also translating Alexander Pope's Essay on criticism into Latin, probably also for Brindley. Gahagan, in his own words, said later: ‘I undertook to translate Mr Pope's Essay on man’ (Old Bailey online).
He clerked for a Mr Ansel in Gray's Inn, having possibly acquired some legal education in Dublin. Entering the underworld of the capital, Gahagan became involved in a scheme suggested to him by Hugh Coffey, whom Gahagan had known since his childhood in Ireland. Joined by Terence Conner, they sought to ‘diminish the current coin of the realm’, melting filings down for sale to gold- and silversmiths. After failing to vary their routine procurement of gold coins from bank tellers, the gang came to the attention of the authorities. On arrest, Coffey informed on Gahagan and Conner, who were tried at Newgate (later the site of the Old Bailey) on 13 January 1749 for high treason. During his imprisonment Gahagan published Latin translations of Pope's (The) Temple of Fame and (The) Messiah, which he dedicated to the duke of Newcastle, the then prime minister, hoping for a grant of clemency. He addressed Prince George in the same vein; however the pair were executed at Tyburn (near Marble Arch) on 20 February 1749.