Last night, as the audience settled into the Westside Theatre after a rainy trudge to Forty-third Street for a performance of “Satchmo at the Waldorf,” a woman approached the front of the stage to make an ominous announcement. John Douglas Thompson, the star of this one-man show, was incapacitated by a pinched nerve in his shoulder. His understudy, Michael Early, would take his place. (Alec Wilkinson wrote about John Douglas Thompson in the magazine in 2012.)

There was a general murmur of discontent. It was a classic theatregoer’s conundrum—insult the new guy by leaving, or stay and see what he’s got—but with a little extra bite: the play is a ninety-minute monologue, and Thompson performed the role to great acclaim in the show’s previous runs. To make matters worse, this was Early’s first day running through the full production, and he would be performing with a script in hand. A woman in my row huffed out; a group of three left and then returned, choosing seats a few rows back, but everyone else stayed put. The lights went low. Wait and see.

Early appeared onstage, a solidly built man whose face is a contradiction: he’s got a definite, shapely mouth that frowns, and large, secretive eyes that smile. Here was Armstrong, winded and exhausted after playing to a crowd at the Waldorf-Astoria. The year was 1971, he was near seventy. We’re in his dressing room—diminutive upholstered sofas, pill bottles, a huge mirror, and a record-player. He hobbles across the stage and collapses onto a sofa, reaches for a mask connected to an oxygen tank, and takes two deep breaths. The audience breathed in, too, because we were nervous about the impending judgment: Would we beam good will toward this actor or withdraw our support? The first impression of a performer is important, and Early was convincingly stooped, lumbering yet graceful, but with a tremor of nervousness.

Early’s voice is rich, with a little gravelly rumble underneath. The first line of the play is “I shit myself today,” and the way Early spoke it gave the impression of Louis Armstrong talking, with resigned good humor, not a terrified actor who hadn’t even had time to master his lines. Armstrong discussed his exhaustion from a lifetime on the road. Now he was playing the Waldorf, triumphant. He could go upstairs and sleep in his opulent suite, but for much of his life, on tour three hundred nights a year, he’d played in hotels and restaurants where they wouldn’t serve him.

The play, which Terry Teachout adapted from his biography of Armstrong, is about the man’s generous essence, which is hard to locate, because his persona is complex and slippery. He was a black man who popularized jazz for white audiences, putting the management of his career into the hands of a venal white man called Joe Glaser; he was a genius often accused of selling out by black musicians of the next generation. The center of the play is Armstrong’s relationship with Glaser. Early had to embody both men, who tell the audience parallel stories of their forty-year partnership.

As Glaser, Early stood upright, quick on his feet, his voice nasal and commanding. Glaser is self-aggrandizing and unapologetically vulgar, talking about Armstrong as his cash cow—and yet he admired Armstrong’s abundant good nature, and understood early on that he could be a pathbreaking performer, beloved by all. He pushed Armstrong to simplify his music, to play for white audiences, even in the South, wearing that huge, brightly lit smile that some people thought was minstrel-like. Armstrong called his manager Mr. Glaser for forty years, and almost never contradicted him, yet it emerges in the play that Armstrong was quietly in control. Glaser managed all the dirty work so that Armstrong’s concentration could remain pristine. He was sealed inside his musical world, and never had to negotiate with anyone about money. (In a sad twist, Glaser screwed Armstrong in the end.)

Teachout’s Armstrong, in Early’s portrayal, is one of the lucky few with a joyous temperament: he loved easily, gave money away freely. Early’s Armstrong glows with good feeling. He was the sort of man whose memories of the Colored Waifs’ Home, a facility that he stayed in for a time as a boy in New Orleans, are laced with the smell of a honeysuckle bush outside his window and the pleasures of leading the brass band. But Armstrong was a joyful man in an ugly time, and his natural savoir-faire coexisted alongside bitterness that his white musician friends never invited him to their homes, and that, when touring in the South, he had to eat his meals on the bus, because restaurants wouldn’t serve him. He was enraged by younger black musicians who kissed up to him in person but called him an Uncle Tom behind his back. In the play, there are three interludes in which Early plays Miles Davis talking smack about Armstrong on the radio. Early’s Davis has a sneering cool, his movements as slithery as a lizard’s.

All this history is conveyed in a ninety-minute speech during which Armstrong changes out of his fancy stage clothes and into casual ones, takes apart and packs up his horn, plays some records, and speaks a few thoughts into a tape recorder. (Armstrong kept a kind of ongoing recorded diary.) With so little stage business to ornament the action, and no chemistry generated by other actors, it’s the kind of distilled performance that thrills and terrifies, or obviously falters. Early was mellowly authoritative—he improvised, as Armstrong would have, when he couldn’t quite get back to the script in time. Though he had to turn the pages, the act seemed synonymous with Armstrong’s searching through the catalogue of his memories. At the end, the audience shouted and applauded with real feeling, and when Early took a bow he shared with us a look of relief. We’d all participated in a delightful pact: we’ll watch you catch this curveball, you’ll pretend like catching it is nothing.

Armstrong was a happy virtuoso; so was Early, when I spoke to him briefly after the performance. He hadn’t had to wing it like this since he was in his third year at Yale Drama School. (He’s now in “early middle age,” as he put it.) Was he nervous? “I’ve never done a one-man show, and I’ve never understudied a one-man show. This is all completely new territory. I mean, I’ve played Hamlet, I’ve played Prospero, I’ve just finished doing Creon, in ‘Antigone,’ and he goes on and on and on and on, but that’s different, because there’s dialogue.” Early chuckled. “When you are the only person up there, you’re exposed.”

He professed huge admiration for Thompson, and said that he worried, watching Thompson rehearse day after day, how he himself would transform the role, make it his own. “You can’t imitate someone. I mean, you can try, but it’s a futile task anyway. You have to ultimately take ownership.” He’d sweated, yelled, cursed, sung, whispered, raged, reminisced—Armstrong had been his for ninety minutes, and tomorrow he’d have to give it all back. And here’s the mad generosity of the understudy: he didn’t mind. He laughed, and ducked out into the rain.

Photograph: O&M Co.