Gielgud was both a pioneer of modern theater and the last of England’s great classical actors, the heir to David Garrick, Edmund Kean, William Macready – and Ellen Terry, his great-aunt. The soliloquies in his 1934 “Hamlet,” more musings than declamations, led one critic to predict, “It will be Mr. Gielgud’s voice in the future that we shall hear as the Prince of Denmark.” In the 1935 “Romeo and Juliet,” he and Olivier took turns as Romeo and Mercutio, inviting decades of comparisons. Olivier saw Gielgud as “all spirituality, all beauty, all abstract things; and myself all earth, blood, all base things.” Unlike Olivier, Gielgud at first resisted avant-garde theater. He talked Richardson and Guinness out of appearing in Samuel Beckett’s “Waiting for Godot,” which he called “a load of old rubbish.” But roles in plays by Edward Albee and Peter Shaffer led up to his triumphant 1975 appearance with Richardson in Harold Pinter’s “No Man’s Land”; his very last work, just weeks ago, was filming Beckett’s late minimalist play “Catastrophe.”

Until the 1970s, Gielgud appeared in few films. “I hate to fail,” he said, “so I stuck to the stage.” But his role as a dying novelist in Alain Resnais’s “Providence” (1977) – his own favorite film performance – put to rest the notion of Gielgud as some antique personification of spiritual beauty. “There was nothing lyrical or old-fashioned about him,” recalled the actor Ralph Fiennes, who saw it at 16. “He was so courageous, direct and ruthless.” And most moviegoers remember him as the foulmouthed butler in the 1981 Dudley Moore comedy “Arthur,” the Oscar-winning part he turned down twice because he found the script “rather common.”

You can watch the elderly Sir John plying his craft on film and videotape – “Chariots of Fire,” “Gandhi,” “Brideshead Revisited,” old Paul Masson wine commercials – but little has been preserved of the essential Gielgud, a creature of the stage, not the studio. We have only written accounts of his great performances and a few glimpses on film: his Cassius in the 1953 “Julius Caesar,” his Clarence in Olivier’s 1955 “Richard III,” his Henry IV in Orson Welles’s 1966 “Chimes at Midnight.” You can hear his voice alone in audio productions of “Measure for Measure” or “The Winter’s Tale,” or the 1994 BBC radio version of “King Lear” – he was nearly 90 – in which he sounds utterly terrified, utterly terrifying. But those who heard him in person say that recordings never captured it. The best of him is unrecoverable: in this he has more in common with the Garricks and Keans, whose work lives only in memories of memories, than with performers in the overdocumented present. John Gielgud came from an age which accepted that theater exists for moments that happen before our very eyes and can never come again, and that the actor’s lot is to strut and fret his hour upon the stage and then to be heard no more.