Sir Arthur John Gielgud, OM, CH was an English actor and theatre director whose career spanned eight decades. With Ralph Richardson and Laurence Olivier, he was one of the trinity of actors who dominated the British stage for much of the 20th century. A member of the Terry family theatrical dynasty, he gained his first paid acting work as a junior member of his cousin Phyllis Neilson-Terry's company in 1922. After studying at the Royal Academy of Dramatic Art (RADA), he worked in repertory theatre and in the West End before establishing himself at the Old Vic as an exponent of Shakespeare in 1929–31.

Gielgud was born on 14 April 1904 in South Kensington, London, the third of the four children of Frank Henry Gielgud and his second wife, Kate Terry-Gielgud, née Terry-Lewis. Gielgud's elder brothers were Lewis, who became a senior official of the Red Cross and UNESCO, and Val, later head of BBC radio drama; his younger sister Eleanor became John's secretary for many years. On his father's side, Gielgud was of Lithuanian and Polish descent. The surname derives from Gelgaudiškis, a village in Lithuania. The Counts Gielgud had owned the Gelgaudiškis Manor on the Nemunas river, but their estates were confiscated after they took part in a failed uprising against Russian rule in 1830–31. Jan Gielgud took refuge in England with his family; one of his grandchildren was Frank Gielgud, whose maternal grandmother was a famous Polish actress, Aniela Aszpergerowa.