Terence Francis MacCarthy (born 21 January 1957), formerly self-styled Tadhg V, The MacCarthy Mór, Prince of Desmond and Lord of Kerslawny, is a genealogist, historian, and writer. Born in Belfast, Northern Ireland, he is a resident of Morocco. His last name is sometimes published as McCarthy.
In 1992 MacCarthy gained Chief of the Name recognition as the MacCarthy Mór. He worked to organise an affiliation of clan associations in Ireland and North America, building on heritage tourism. He also became active in the International Commission on Orders of Chivalry (ICOC), in which position he promoted an order known as the Niadh Nask. His claims were challenged in 1999 by The Sunday Times, which had conducted an investigation of his ancestry and claimed his father was an ordinary working man in Belfast. Later that year, recognition of MacCarthy was withdrawn and he resigned the title. His younger brother claimed it, but in 2003 the government discontinued the practice of granting courtesy honors to Chiefs of the Name.
On 28 January 1992, the Irish Genealogical Office conferred courtesy Chief of the Name recognition to Terence MacCarthy as the MacCarthy Mór, the title of the chief of the MacCarthy sept or clan. The title literally means "the great MacCarthy." The MacCarthys had been princes of Desmond, and earlier, through the Eoghanacht of Cashel, the kings of Munster. Terence MacCarthy claimed the title based on tanistry rather than primogeniture, and said that his father renounced the title in his favour in 1980. He led an affiliation of MacCarthy clan associations in Ireland, Canada, and the United States, which appealed to heritage tourism trends of the time. MacCarthy instituted a quasi-chivalric order, the Niadh Nask, and conferred titles of nobility on his supporters.