Slevin, ( John) Gerard (1919–97), heraldist and dramatist, was born 1 November 1919 in Cork, son of John Slevin, motor mechanic, of Wellington Rd, Cork, and Bridget Slevin (née Kennelly). His father, who hailed from Co. Laois tenant farmers, worked with the Irish Omnibus Corporation. Gerard was educated at North Monastery CBS and UCC, taking an MA summa cum laude in philosophy and English (1941). After lecturing at St Patrick's teacher training college, Drumcondra, Dublin (1941–4), he entered the civil service; despite no prior interest in heraldry, he was selected via competition to assist the newly installed chief herald, Dr Edward MacLysaght (qv), in the genealogical office, Bedford Tower, Dublin Castle. After serving as deputy chief herald (1944–54), he succeeded MacLysaght as chief herald of Ireland, becoming the longest-serving occupant of the office (1954–81). One of three national heralds named to a vexillogical committee to devise a common emblem for the Council of Europe, he persuaded his colleagues to eschew religious iconography, such as the Christian cross, as inappropriate. His own design of a circle of twelve golden stars on an azure field was selected by the committee in 1954, and formally accepted by the council in December 1955. With blue chosen as a colour common to the flags of many European countries, the twelve stars represented not individual states but such associations as the zodiac and a clock face, suggesting ideals of universality, harmony, and evolution through time. Adopted in 1985 for the flag of the European Community (latterly the European Union), Slevin's design attracted wide acclaim in heraldic circles, leading to his being awarded membership of the Académie Internationale d'Héraldique, the only Irish person so honoured.
During his tenure as chief herald, several hundred patents of arms were issued to Irish public bodies, including civic and municipal authorities, and to individuals of Irish descent worldwide. On behalf of the Irish government, he confirmed the Irish connections of such notables as US presidents Kennedy, Nixon, and Reagan, French president Charles de Gaulle, and Princess Grace of Monaco. His coat of arms for President Kennedy, combining the ancient arms of the Kennedy and Fitzgerald families, won renown as a masterpiece of heraldic design. While possessing a keen sense of graphic impact, Slevin was not a great draughtsman, and he employed the noted heraldic painter Myra Maguire to execute the designs that he created. He oversaw expansion of genealogical office services, instituting an advisory service and team of research assistants for the growing numbers – especially within emigrant communities abroad – seeking to trace Irish ancestry. He established a committee to catalogue churchyard memorial inscriptions as an archival resource, meant to redress the loss of state records in the 1922 Four Courts fire.
Slevin won first prize in successive years in the 1950s for entries in the oireachteas drama competition, both plays being subsequently produced at the Abbey theatre. He wrote a detective novel in Irish, and contributed numerous articles to learned journals, chiefly on medieval heraldry and Anglo-Irish families. Erudite and possessed of great presence, courtesy, and wit, he was an engaging speaker. Resident in south Co. Dublin, he was active in amateur dramatics, local history societies, and the ecumenical movement; his recreation was long country walks. He married (1950) Millicent Nolan; they had three sons. He died on 18 January 1997.