Dix, Ernest Reginald McClintock (1857–1936), solicitor, book collector, and Irish language enthusiast, was born 8 April 1857 in Dublin, elder son of Henry Thomas Dix (1825–1902), a prominent solicitor, and his wife Emma Patience, daughter of an army officer, Henry McClintock of Dundalk, Co. Louth, and sister of Sir Francis Leopold McClintock (qv). His great-grandfather was Ebenezer Dix (1748–1824), who arrived in Dublin from England in 1779 and became secretary of the Farming Society of Ireland. A sister of Ebenezer was mother of Thomas Dix Hincks (qv). Two of Ebenezer's three sons and four of his grandsons became lawyers. Ernest Dix was admitted as a solicitor in 1879, having been apprenticed to his father, whose partners he and his younger brother, Leopold McClintock Dix, eventually became. The firm practised in Dublin from an office at 61 Upper Sackville Street, and later at 24 Clare Street.
Ernest Dix was best known for his love of old books, of which he was an energetic collector. Between 1891 and his death he published over 200 articles on aspects of Irish bibliography, a list of which occupies eighteen columns in Hayes's Periodical sources. His most important work was Catalogue of early Dublin-printed books, 1601 to 1700 (5 pts, 1898–1912). In 1908 he was elected a member of the RIA, to which he read no fewer than sixteen papers (1900–21). In 1919, with Séamus Ó Casaide (qv) and others, he founded the Bibliographical Society of Ireland, becoming its first president. Dix remains the authority on Irish early provincial printing. He gave a large part of his collection to the NLI and parts to other libraries. He had no interest in the content of his books – his interest was in preserving and listing them. An enthusiast for the Irish language, he edited an Irish translation of the Psalms of David (1912) and translated into Irish the communion service of the Church of Ireland (1913).
Ernest Dix died on 2 May 1936 at his home in Butterfield Lane, Rathfarnham, Co. Dublin, survived by his wife Elizabeth Rachel, daughter of Graves Leech, a solicitor to the land commission. Known as Úna Bean Uí Dhíosca, she was also an enthusiast for the Irish language. They had two adopted sons, one of whom, Peter (1925–2007), became an actor and, as a member of the RTÉ Players, took part in over a thousand radio plays.