The obituaries for Stephen Sondheim have done full justice to his unique contribution to musical theater, and his sometimes acerbic view of his fellow practitioners. What is less well known is that he was a tireless if exigent mentor to burgeoning talents in that sphere; many young composers on both sides of the Atlantic have benefited from his unsparing but inspiring tutelage, a tough-love regime freely offered and unstintingly applied, often as a result of a letter or an e-mail received after a performance he had admired.

My colleague Kevin Malpass received just such a letter after Sondheim had seen the 1979 West End production of Tom Stoppard’s Artist Descending a Staircase: “Dear Kevin Malpass—I told Tom, and he suggested I convey it to you, that I thought your score absolutely wonderful: full of atmosphere, originality and surprise. I think you gave this play a tone it might not have had otherwise. It made me envious. Stephen Sondheim.” Here he was, on the brink of 60, composer of a succession of proclaimed masterpieces, holding out a hand to a fledgling composer.

Sondheim has sometimes been portrayed as severe, private, reclusive. Nothing could have been further from the truth. I knew him for more than 40 years, having been introduced to him by Peter Shaffer at the time of Amadeus; to my astonishment, he knew who I was, but then, as I swiftly discovered, he always knew everything about the theater on both sides of the pond.

Keeping score.

We would bump into each other at shows and at parties. He came to see my shows, I went to his, and finally one day when I found myself in New York I was emboldened to ask him to have dinner with me. I was about to direct Die Fledermaus in Glasgow, and wanting to show the young metrosexuals of the Vienna in which the operetta was first performed for what they were, I thought of the characters in Company, the first show of his I had ever seen, an instantly recognizable group portrait of modern urban life, and wondered whether he could be persuaded to write new lyrics for Johann Strauss II’s piece. No, he said, he detested opera; it was everything he hated most in the theater. He then revealed an astonishingly wide and deep knowledge of the repertoire.

At some point in our conversation, Lauren Bacall came up to our table and growled at me that she loved this man, pointing at him, but that she didn’t know what she felt about me. After she left, I asked him what she meant by that. “I have no idea what Bacall meant,” he said, “but then, most of the time neither does she.”

As for Fledermaus, he said: “Lyric writing is too difficult and upsetting for me not to have composing go with it. Truthfully.” He then, typically, gave me the address and phone number of the author of a recent version which he admired. He was happy to function as the central switchboard of the musical theater, connecting people, his endorsement a guarantee of quality.

Our friendship grew, but we never worked together. Once, he asked me to take part in a workshop for the show then known as Wise Guys, which became Bounce and ended up as Road Show, before closing after a thin three-month run. With the exception of “Send in the Clowns,” Sondheim’s scores are fiercely demanding, quite beyond my poor capacities. I declined, thus keeping our friendship intact.

Lee Remick, left, and Lauren Bacall backstage with Stephen Sondheim after the opening of the musical Side by Side by Sondheim on Broadway in April 1977.

Writing proved to be a bridge between us. Surprisingly, for a man in the grip of logomania, Steve read few books, or so he claimed. I sent him the first volume of my Orson Welles biography when it came out, in 1995; he wrote to me in 2000 to tell me that he’d finally read it. To my considerable relief, he enjoyed it: if you only read two books a year (his average, he claimed), they’d better be good. He had just seen Citizen Kane again, he told me, and had suddenly been struck by a logical impossibility: “Kane whispers ‘Rosebud’ into a completely empty room and dies before the nurse enters … Unless something was cut in the print I saw, the McGuffin is only a Guffin, if that.” Then he added, “Maybe I’d better stick to trivial murder mysteries.” He was widely known to be obsessed with murder stories. He had a deeply mathematical brain, as one hears clearly in the extraordinary structures, verbal and musical, he elaborates in his scores.

He persisted with the successive Welles volumes, spurring me on: “Please let my enthusiasm for Volume 1 of O Welles encourage you to push ahead on Volume 2. It’s so rare that I enjoy reading anything, and I’d like another excuse.” When Volume Three eventually arrived, he said: “I had no idea (did you?) the opus would be so magnum. Doorstoppers they may be, but your doorstoppers I read eagerly.” A couple of years later I mentioned that I was acting in a film, and he wrote: “I don’t know what you’re doing acting, anyhow. You should be writing. Or perhaps simultaneously you are. I hope.”

Sondheim has sometimes been portrayed as severe, private, reclusive. Nothing could have been further from the truth.

In time, he produced two books himself, the superb Finishing the Hat and Look, I Made a Hat, both of which combine autobiography with penetrating and often self-critical analysis of his craft (and that of his fellow songwriters). I reviewed the first book enthusiastically in The Guardian. “I just read your review,” he wrote to me. “When do we set the wedding date?” Not so long after, he really did, somewhat to everyone’s surprise, get married, to Jeffrey Scott Romley. Not knowing this, I had written to Steve in an e-mail that I trusted that he was in radiant form: “I am indeed,” he replied. “I got married on New Year’s Eve.”

The next time I saw him was with Jeff and another of his talented protégés, the Belfast composer Conor Mitchell, and he was clearly basking in the relationship with Jeff—Steve, musical theater’s most savage satirist of marriage. Jeff, a triathlete, was in training for a mega-marathon, his eyes sparkling as he described the impossible demands it would make on him. I wrote to Steve, “As an unathlete, I’m still reeling at the thought of what he’s attempting. I’d rather spend a month in Guantánamo Bay.” Steve wrote back: “As for Guantánamo Bay, I think Jeff is going to swim it.”

On that occasion, he talked about his work in progress: an adaptation of two films by Buñuel. I interrogated him about his progress: “Outside of the fact that his films lack story and character (but who needs them?), no problem. But style he has.” He seemed utterly undaunted by the fact that one of the two films, The Exterminating Angel, had just been made into a highly successful opera by Thomas Adès. “At this rate, by the time I’ve finished, they’ll have forgotten all about the opera.” He ended with “Hope to see you again soon. I expect to be in London before the end of the year. If so, I’ll give you fair warning if you want to flee the country.” I stayed.

He was here to receive an honorary degree from the Royal Academy of Music. It was a touching occasion, if a little peculiar—peculiar mostly because, after rousing performances of a selection of his songs by the student orchestra and chorus, Steve appeared onstage clothed in the parti-colored medieval cap and gown which the honored are expected to wear. Unsmart casual would be the best description of his normal attire, and at the academy he gave the impression of having been roused in the middle of the night by armed guards, forced into fancy dress, and conveyed to a place of public humiliation.

Cap askew, gown slipping off his shoulders, he sat on a chair on the stage at an odd angle and listened with apparent remorse to the summary of his life and work, beautifully written by Jeremy Sams, the theater director, and nobly delivered by the Beethoven scholar John Suchet. Steve’s remorse seemed to grow with every passing reference. There was a little more music, and then he left the stage while his friends and admirers repaired to a room to greet him. I happened to be the first back and was astonished to find him in tears. “Those kids,” he said, “singing and playing my stuff so beautifully. It gives me so much hope.”

He turned 90 in March 2020, to huge fanfare across the Western world. That very month I was in New York, rehearsing for a musical based on the Britney Spears back catalogue, and we had arranged to have supper. I had only been rehearsing for two and a half days when the great axe fell, rehearsals were suspended, and the Chicago run was canceled, and soon I was on a plane back to London. Once I got back, I sent him a copy of a book about London theaters which I had just brought out. The only package I could find was shiny and black. I sent it to him express, telling him about the aborted musical and saying, “Eschewing anything as vulgar as actually greeting you on the day itself, I have finally sloughed off the paralysis of the Covidian quotidian and posted you a small token of deep affection and profound admiration.” “Covidian quotidian indeed,” he replied. “It took a plague to get you to reveal the Noel Coward within. But we all knew it was there. Thank you for both the greetings and the compliments. Next time you’re in NYC, however, please put on your rubber gloves and give me a call. The black parcel hasn’t arrived yet, although apparently (I’m in Connecticut) a hearse has been waiting across the street from my house for a couple of weeks now. Thank you in advance. Good luck with the musical, although remember that Britney Spears is an anagram of Presbyterians. And coronavirus is an anagram of carnivorous. I leave you to draw your own conclusions. Stephen Sondheim (age 90). Be sure to notify me when you’re about to return. We’ll keep the food warm.”

A week or so later, he sent this: “Dear Simon—The mysterious parcel arrived. Thank you so much. You can’t imagine how comforting it is for me to know that there are theatres even older than I. Say hello to The Queen’s for me, or whatever they’re calling it for the nonce. And thank you again. Steve.”

The Queen’s Theatre is now, and for the foreseeable future, the Sondheim Theatre.

Simon Callow is an actor and director, and the author of several books, including an acclaimed three-volume biography of Orson Welles