Yesterday's memorial for John Wood, who died last August aged 81, was a feast of celebratory anecdote and appreciation, led from the front by Tom Stoppard - "he truly was my favourite actor" - and attended in St Paul's Church, Covent Garden, by Maggie Smith, Vanessa Redgrave, Michael Gambon and a host of talented worthies.

These included three National Theatre artstic directors (Peter Hall, Richard Eyre and Nicholas Hytner), three Uncle Vanyas (Gambon, Simon Russell Beale and Roger Allam), RSC supremo Terry Hands, and a supporting cast of the  best in the business: Sinead Cusack, Sara Kestelman, Adrian Scarborough (Silence to Wood's Shallow), Patrick Godfrey, Elliot Levey.

Everyone knew what a great actor Wood was, except, perhaps, the general public. His realm was exclusively the stage, and at the high end of the market. He wasn't a film star, and rarely appeared on television. Temperamentally, he was both haughty and ascetic. And he was fearsomely, ferociously clever... and hugely funny.

As Stoppard said, he seemed to know something about everything and, when he spoke, gave the impression of knowing everything about something. He was passing a college chapel in Oxford with a musicologist friend and identified the emanating strains as Scarlatti. It's not Scarlatti, said the friend, I assure you, I know the entire works.  Wood remained adamant, insisting on settling the matter.

They went inside and discovered that the music in rehearsal was indeed Scarlatti, but a piece that had only recently been unearthed from the archives. The way Stoppard told it, we could have been listening to a brilliant new short comedy.

Same with his story about the shoes. One day, Wood was delighted with a new pair and asked Stoppard whether he thought they were very expensive or very cheap. Stoppard, stymied, bought time with a long pause. "You see," said Wood, "that's how wonderful they are, you can't tell. Come on, very expensive or very cheap?"  

The son of a Prague shoe salesman finally settled on "medium-priced," and said that he honestly thought that this was the only time in his life he ever saw John Wood lost for words.

Wood was a perfectionist, Stoppard said, and insisted on perfectionism in everyone else. When he played Guildenstern in Stoppard's play in New York, he was prone to giving the Rosencrantz actor notes not only backstage after a performance - which was bad enough, Stoppard thought - but onstage as well, during the performance.

The note-giving habit extended to the audience, confirmed Hytner in his analytical and affectionate tribute. He once turned impatiently on a dosy mid-week matinee house during the run of Travesties at the Aldwych with a loudly spluttered, "Oh do keep up!"

And when he played Prospero - easily the best I've ever seen - in Hytner's RSC production, the long exposition scene with Miranda was littered at one Thursday matinee with volleys of bronchial coughing in the stalls.

Wood stopped dead in his tracks and turned again. "Would you please stop coughing," he yelled with a rasping ferocity. The audience was instantly cowed and fell utterly silent - until Desmond Barrit came on as Trinculo in full jester costume and, raising his hand to his mouth, produced a tiny, throaty "ahem." 

Russell Beale read one of Henry Carr's great speeches in Travesties, and the mighty Gambon shivered delectably as Falstaff in the orchard scene, with Scarborough playing Shallow and Levey a dumbstruck Silence. Then a recording of Prospero's farewell, in which that mighty, metallic voice let rip over several octaves, untouched by Gielgudian sentiment or self-pity, truly terrifying, truly extraordinary.

"I don't think you could get away with that today," muttered Roger Allam in his pew, visibly shaken. We were all as silenced as the offending matinee audiences.

Then, as we filed out, Russell Beale let slip a moment of incomparable Wood magic: in Love's Labour's Lost, as Don Armado, he said of someone that he was "out of his pavilion," and accompanied the line with a screwy rotation of his index finger by his right temple. Russell Beale was shaking like a mirthful jelly at the very thought of it. And that's what it was: a thought, an idea, of such penetrating originality that only a genius of an actor could have come out with it.   

The party repaired to a private room in the Delaunay restaurant on the Strand, hard by the Aldwych where Wood enjoyed some of his greatest triumphs. Michael Billington told me that his life had been blighted with guilt ever since, over dinner in New York with Wood, and after seeing his brilliant performance in Deathtrap, he insisted that the actor's next project should be Richard III. For reasons that nobody's ever quite fathomed, this proved the biggest flop of his career. Which only goes to show that you should never listen to a critic.

For my own part, the first full-length full-dress overnight review I ever had to write was of that first performance of Travesties, which was a bit like having a first driving lesson on the M1 during the rush hour. No playwright is more daunting than Stoppard, but the salvation for a critic lies in the roles he writes for actors. And such actors, among whom Wood was supreme, give the poor benighted critic something to latch onto in the detail, passion and thrilling articulacy of their performances. Reviewing is infinitely duller without him.