De Valera, Ruaidhrí (1916–78), archaeologist, was born 3 November 1916 in Dublin, fourth son among five sons and two daughters of Éamon de Valera (qv) and Sinéad de Valera (qv) (née Flanagan). Educated initially at Blackrock College he entered UCD in 1935, where he was active in Irish-language circles and graduated with a BA in Celtic studies (1939). He served in the Irish army (1940–42), and the following year (1942–3) became a lecturer in Old Irish and Welsh at Maynooth college, before returning to postgraduate study at UCD. In 1945 he was awarded an MA for his thesis on the megalithic tombs of north-east Clare. Further intensive studies of Irish megalithic tombs followed, and in 1947 he was appointed as archaeology officer of the ordnance survey, having served a year in that office as place-names officer. De Valera's time with the ordnance survey resulted in ground-breaking studies in collaboration with Seán Ó Nualláin, and in Surveys of the megalithic tombs of Ireland (3 vols, 1961, 1964, 1972), and served as inspiration for his Ph.D. thesis (1954), which introduced new and stimulating ideas into a subject previously dominated by generally accepted doctrines.
In November 1957 he was appointed professor of Celtic archaeology at UCD and began to oversee major expansion of the department, making it the largest school of archaeology in Ireland, as well as fostering advances in the study of prehistory and in writing and lecturing in Irish, completing pioneering work in devising an appropriate archaeological terminology. He served as vice-president of the RSAI as well as being elected dean of the faculty of Celtic studies in UCD and a member of the senate of the NUI, representing graduates. He had a great passion for the Irish language and for Irish unity, and served as president of An Comhchaidreamh, the inter-university Gaelic organisation. Academically, he was regarded as having an exceptional speculative imagination, realising that the megalithic tombs of Ireland provided a significant key to a major area of prehistory. Particularly committed to evening students, the concept of academic freedom, and the independence of UCD from the encroachment of government and big business, de Valera opposed the plans of Donough O'Malley (qv) to merge UCD and TCD. Sceptical of bureaucracy, he did little to court student popularity, to adapt to prevailing trends, or to conceal his individual and often unfashionable views. However, he aligned himself closely with the Wood Quay protesters. He died suddenly 28 October 1978 in Enniskillen at an academic conference, in the aftermath of a debate on megalithic tombs, surrounded by many of his former students.
He married (June 1948) Eithne Smyth, solicitor, from Downpatrick, Co. Down; they had two sons and a daughter.