Updated November 26, 2021 at 6:18 PM ET

Stephen Sondheim, the Pulitzer Prize- and Tony Award-winning Broadway songwriter has died at age 91. His death occurred early this morning, according to Aaron Meier at DKC O&M, the producers of Company on Broadway.

Sondheim would have been the first to tell you he was a Broadway baby. As a teenager, he learned about theatrical songwriting from a master – Oscar Hammerstein, the author of Showboat and Oklahoma!, among others – and, by the time Sondheim was twenty seven, he had his first show, West Side Story, on Broadway.

Even though he only wrote lyrics to Leonard Bernstein's music for West Side Story, it was the beginning of a remarkable career in which Sondheim – as lyricist and composer – elevated what was, essentially, a lighthearted, optimistic commercial entertainment into an art form.

Sondheim's shows, with their intricately crafted scores, reflected his restless curiosity about human nature – from the barber exacting murderous revenge in Sweeney Todd, to the struggling painter Georges Seurat in Sunday in the Park with George. Sondheim looked at contemporary marriage – and ambivalence – in Company, the culture clash between 19th-century Japan and the United States in Pacific Overtures, the dark side of fairy tales in Into the Woods, and even surveyed presidential Assassins.

Over the course of a career which stretched for more than 60 years, Sondheim received both critical praise and brickbats for his adventurous work. Frank Rich is a columnist for New York Magazine and former drama critic for The New York Times.

"Perhaps no one more than Sondheim contributed to just keeping the form alive of what had been the classic Broadway musical. He reinvented it," Rich says. "He kept it fresh, interesting, figuring out new ways, to, you know, muck around with it for each show."

Sondheim was notoriously painstaking in his craft – and actually published two large books featuring his lyrics and explaining his writing process. He told WHYY's Fresh Air in 2010 that before he wrote a bar of music or came up with a rhyme, he needed to consult the show's script.

"I always write after the librettist has started to write a scene or two," Sondheim said, "so that I can divine and imitate the style the writer is using, both in terms of dialogue and approach and getting to know the characters as he is forming them."

And that specificity made performers like Bernadette Peters love his work. "He writes as if he's an actor, as if he's playing the role ... If you have a quarter note, there's a reason – the quarter note helps you express what you're feeling at that moment."

"Send in the Clowns" was the only hit song Sondheim ever wrote. It's from his show A Little Night Music, which itself was a modest success. The musical was originally directed by Hal Prince, one of Sondheim's most frequent collaborators.

Laurence Maslon, who co-produced the PBS series Broadway, says their envelope-pushing work was never really commercial.

"Not a single show he ever wrote ran more than a thousand performances," Maslon observes. "And they play all over the world and they're revived every five minutes, but they simply don't have that commercial traction, that even Hammerstein had back in the day."

In fact, starting in the 1980s, Sondheim exclusively developed his work at not-for-profit theaters, a period that also saw the start of his collaborations with James Lapine.

"My first not-for-profit show was Sunday in the Park with George and that was because of Lapine," Sondheim told Fresh Air. "And, of course, it was such a pleasure, compared to doing it on Broadway. I mean, the lack of pressure, not having to worry about everything from budget to backers, and it was just fun to do. And that's the way theater should be done – just for the love of it."

Sunday in the Park with George, written with James Lapine, eventually migrated to Broadway, where it won a Pulitzer Prize — but again, it wasn't a commercial success. Like many other artists who are now considered masters, it took a while for Sondheim's shows to catch on, and for Sondheim to move from a cult figure to a cultural icon. He said he was always keenly aware of making an impact with his writing.

"I'm interested in the theater because I'm interested in communication with audiences," Sondheim said. "Otherwise, I would be in concert music. I'd be in another kind of profession. I love the theater as much as music, and the whole idea of getting across to an audience and making them laugh, making them cry — just making them feel — is paramount to me."

And the feelings he stirred in audiences will continue well beyond his death.

The attached audio story was produced by Bob Mondello.

Copyright 2021 NPR. To see more, visit https://www.npr.org.