O'Brien, Henry (1808–35), antiquary, was born in Co. Kerry, and was apparently third son of Bryan O'Brien of Dromin and Ellen O'Brien (née MacCarthy), who were minor catholic gentry; if he was, he entered King's Inns in Dublin in 1828, having been educated in TCD. O'Hart's Irish pedigrees (5th ed. 1892), quoted in the introduction to the 1898 edition of O'Brien's Round towers, gives his first names as ‘Turlogh Henry’. Though there is no record in the list of alumni of TCD, he is said to have graduated BA from TCD in 1831. According to the occasionally unreliable Francis S. Mahony (qv), O'Brien was tutored by the distinguished mathematician Charles Boyton (qv). His earlier education, in a remote and rather impoverished area, was apparently neglected; he wrote: ‘I was twelve years of age before I ever saw a Testament in any language.’ He was brought up as an Irish-speaker. Much of his knowledge appears to have been acquired by self-education; he read avidly, and probably uncritically; a later editor remarks on O'Brien's elementary errors in Latin and Greek. In spite of this, he was for a time private tutor in the family of the master of the rolls in England.
In 1832, on very short notice, O'Brien enthusiastically wrote a dissertation on the round towers of Ireland in an attempt to win the RIA's Cunningham gold medal and a £50 prize offered by the Academy to the person whose work would finally explain the origin of what were then regarded as enigmatic structures. Other competitors included Marcus Keane (1815–83) and the eventual recipient of the 1833 medal, George Petrie (qv). O'Brien was awarded £20 as consolation, but he had been so passionately convinced of the importance and accuracy of his explanations and hypotheses that he accused the Academy of unfair adjudication, and unsuccessfully demanded that it should reconsider and award him the prize. Not surprisingly, the Academy refused to publish his essay, which he had hoped would appear in its Transactions.
In 1834 he published an expanded version of his essay as The round towers of Ireland; or the mysteries of freemasonry, of Sabaism, and of Budhism [sic] for the first time unveiled. The subtitle and content of this work make it clear that O'Brien revelled in the speculative romantic approach which had dominated Irish antiquarianism, but was then being replaced by the more critical and empirical approach of men such as George Petrie and John O'Donovan (qv). On the grounds of what he believed to be striking similarities between ancient Ireland and Eastern cultures, O'Brien argued that round towers were of Buddhist origin. Notoriously, he also suggested that they were monuments connected with phallic worship, which he believed to have been associated with Buddhism. Most reviewers rejected O'Brien's theories. Sir William Betham (qv), though he also believed that the towers were of eastern origin, described O'Brien's work as that of a madman.
Henry O'Brien was found on 28 June 1835 dead in bed in a friend's house, in Hanwell, Middlesex, and was buried in the local churchyard. Remarks in obituaries, such as that in the Gentleman's Magazine, appear to allude to O'Brien's disturbed mental state, and it is probably not a coincidence that the Middlesex Lunatic Asylum was located in Hanwell.