Boyd, John St Clair (1858–1918), surgeon, Gaelic Leaguer, and philanthropist, was born at Cultra House, Holywood, Co. Down, only son of John Kane Boyd, co-proprietor of the Blackstaff Mill. He was educated in Paris and Edinburgh before graduating from QCB and the RUI as a doctor in 1886. He worked at the Birmingham and Midland Hospital for Women, the Hospital for Sick Children in Belfast, and the Ulster Hospital for Children and Women, before being appointed as senior surgeon at the Samaritan hospital, Belfast, where he worked till ill-health forced early retirement (1907). On retirement he was appointed honorary consultant surgeon and remained a member of the Ulster Medical Society and the British Medical Association.
A member of the Church of Ireland and a strong unionist, he was a prominent member of the Gaelic League in Belfast. Although never a fluent Irish-speaker, he was the first president of the Belfast branch, was deeply committed to the language, and was perhaps the league's largest financial donor in its first decades. Highly respected by the leaders of the language movement, he was on the platform at the first Oireachtas, in 1899 a member of the Oireachtas organising committee, and from 1900 a member of the executive committee. He travelled across Ulster with other members of the League to Irish-speaking areas and fostered support for the organisation as non-political and non-sectarian, before drifting from centre-stage after the decline in his health. Having inherited his father's fortune, he was a man of considerable wealth and was benefactor to a wide range of organisations such as the Belfast Natural History and Philosophical Society, the Irish Temperance League, Irisleabhar na Gaeilge, the Irish Texts Society, and the Pipers’ Club, of which he was president.
An art lover with a considerable collection of paintings, he was married to Helen Stevenson of Edinburgh, and lived first at Victoria St., Belfast, and then for many years at Chatsworth House on the Malone Rd, Belfast. He died 10 July 1918 in Belfast.