Stephen Sondheim, whose intricate and impactful lyrics, venturesome melodies, and sweeping stage visions made him a central figure in contemporary American musical theater, died Nov. 26 at his home in Roxbury, Conn. He was 91.

Composer and lyricist Stephen Sondheim, shown in 2018, has died at age 91. Kirsty Wigglesworth/Associated Press

Rick Miramontez, a publicist for the current Broadway production of Mr. Sondheim’s musical “Company,” confirmed his death but did not cite a cause.

In a career spanning more than five decades, Mr. Sondheim was associated with many of the most celebrated and enduring musicals of his time.

He won his initial fame as the lyricist for “West Side Story” (1957), with music by Leonard Bernstein, and followed up by writing the lyrics for Jule Styne’s “Gypsy” (1959). His primary achievement lies in the works for which he created both music and lyrics, including “A Funny Thing Happened on the Way to the Forum” (1962), “Company” (1970), “Follies” (1971), “A Little Night Music” (1973), “Sweeney Todd” (1979), “Sunday in the Park With George” (1984), “Into the Woods” (1987) and “Passion” (1994).

Unlike most of the earlier Broadway songwriters, including George and Ira Gershwin, Cole Porter, Richard Rodgers and Oscar Hammerstein II (the last of whom was his first great mentor), Mr. Sondheim was less interested in creating stand-alone popular “hits” than in fashioning unified works that maintained a firm, near-operatic structural integrity throughout.

To be sure, earlier Broadway productions had aspired to high seriousness, with Jerome Kern and Hammerstein’s “Show Boat” (1927) and the Gershwins’ “Of Thee I Sing” (1931) at the top of the list. Mr. Sondheim not only bound music, lyrics and book inextricably together, but he explored in far greater depths the human condition in all its anxieties and moral complexities.

His characters could be jaded, ironic, self-lacerating and acerbic, defining character traits captured in lyrics to “Now You Know” from his 1981 musical “Merrily We Roll Along.” The character Mary Flynn, an alcoholic critic and writer; sings:

I mean, big surprise:
People love you and tell you lies.
Bricks can fall out of clear blue skies.
Put your dimple down,
Now you know.
Okay, there you go –
Learn to live with it,
Now you know.
It’s called flowers wilt,
It’s called apples rot,
It’s called thieves get rich and saints get shot,
It’s called God don’t answer prayers a lot,
Okay, now you know.

“Without question, Steve is the best Broadway lyricist, past or present,” the playwright Arthur Laurents, who worked with Mr. Sondheim on four productions, once observed. “Steve is the only lyricist who writes a lyric that could only be sung by the character for which it was designed, who never pads with unnecessary filters, who never sacrifices meaning or intention for a clever rhyme, and who knows that a lyric is the shortest of one act plays, with a beginning, a middle and an end.”

Mr. Sondheim’s music was never intended to make the hit parade, but on occasion it did. His most famous single song is the bittersweet “Send in the Clowns” from “A Little Night Music,” which was recorded by Judy Collins a full year after the original production had closed and made the pop charts in 1975 and 1977.

Since then, it has become one of the most familiar melodies in the repertory and recorded hundreds of times. And yet the composer had determined that “Send in the Clowns” would always make its strongest impression when heard in the context of “A Little Night Music,” where it is sung by an aging actress as she reflects upon an unfulfilled love affair (“Isn’t it rich? Are we a pair? …”). Indeed, Mr. Sondheim wrote the song specifically for the limited but affecting voice of Glynis Johns, who created the role on Broadway.

Other Sondheim works explored the difficulties of creating and maintaining romantic relationships (“Company”); a reunion of aging actors in a theater scheduled for demolition (“Follies”); the beginnings of American imperialism in Asia (“Pacific Overtures,” 1976); the creative process as exemplified in the career of the French postimpressionist painter Georges Seurat (“Sunday in the Park With George”); and the history of political murder in the United States (“Assassins,” 1990), complete with roles for John Wilkes Booth, Lee Harvey Oswald and other villains.

All were unusual subjects for commercial theater. “Sweeney Todd,” a ghoulish “musical thriller” that tells the tale of a London barber who slits the throats of his clients and then sells their bodies for meat, might be Mr. Sondheim’s masterpiece. Tim Burton translated it to much critical acclaim into a 2007 film (although those who knew the original play were dismayed by Burton’s many cuts). Still, Mr. Sondheim’s dark humor was not necessarily a universal sell to audiences who wanted tamer fare to accompany their evenings out.

And so Mr. Sondheim’s shows never ran as long and as widely as “Cats,” “Evita,” and “Phantom of the Opera” by Andrew Lloyd Webber, “Les Miserables” by Claude-Michel Schoenberg or “A Chorus Line” by Marvin Hamlisch. Yet few doubted his primacy in the field.

He won the Kennedy Center Honors for Lifetime Achievement in 1993 and was the subject of a “Sondheim Celebration” there in 2002, where six of his works were presented in repertory staging, to exhilarated reviews and sold-out houses; the Signature theater in Arlington, meanwhile, became a major staging ground for many of his works. He and James Lapine shared the Pulitzer Prize for drama in 1985 for “Sunday in the Park With George.”

In addition to a 2008 Tony Award for lifetime achievement, Mr. Sondheim received eight Tonys for his music and several others for his lyrics. In 2015, President Barack Obama awarded him the Presidential Medal of Freedom, the nation’s highest civilian honor.

His influence on other composers is difficult to assess, as his art was so personal, immaculate and unpredictable. There is very little that could be mistaken for Mr. Sondheim in the present-day commercial musical theater, although a revue created from his songs, “Side by Side by Sondheim,” helped inspire Stephin Merritt’s varied and virtuosic three-hour cycle “69 Love Songs” that Merritt created for his group Magnetic Fields.

Mr. Sondheim said he never “wrote down” to his public and mistrusted music that he found too easy.

In his 2010 book “Finishing the Hat” – an anthology of Mr. Sondheim’s lyrics from his student days through “Merrily We Roll Along” – he enumerated the three principles he considered necessary for a lyric writer: “Content Dictates Form; Less is More; God Is in the Details – all in the service of Clarity, without which nothing else matters.”

“What’s hard is simple/
What’s natural comes hard
Maybe you could show me
How to let go
Lower my guard …”
– “Anyone Can Whistle” (1964)

Stephen Joshua Sondheim was born in New York on March 22, 1930, the only child of Herbert Sondheim and his wife, the former Etta Janet Fox, known as Foxy.

Both parents were in the fashion industry, and Stephen grew up wealthy in the San Remo apartment building on Central Park West. An acrimonious divorce in the early 1940s left Stephen living with his mother. He grew to despise her, to the point of cutting off all ties with her and refusing to attend her funeral in 1992.

“When my father left her, she substituted me for him,” he told biographer Meryle Secrest. “And she used me the way she had used him, to come on to and to berate, beat up on me, you see. What she did for five years was treat me like dirt, but come on to me at the same time.”

This period shaped much of his personality and especially his mordant wit. As an adult, he acknowledged a gift from his friend Mary Rodgers by writing back: “Thanks for the plate, but where was my mother’s head? Love, Steve.”

Mr. Sondheim was 15 and attending the private George School in Newtown, Pa., when he wrote his first musical (entitled “By George” and set at the school). He gave it to the playwright and lyricist Oscar Hammerstein II, who was the father of a childhood friend.

“I went home with delusions of grandeur in my head,” he later told the critic Craig Zadan. “I could see my name in lights. Next day when I got up he called and I went over to his house and he said, ‘Now you want my opinion as though I really didn’t know you? Well, it’s the worst thing I’ve ever read.’ And he probably saw that my lower lip began to tremble and he said, ‘Now I didn’t say that it was untalented, I said it was terrible. And if you want to know why it’s terrible I’ll tell you.’ ”

Hammerstein then proceeded to go through every stage direction, every song, every scene, every line of dialogue. “At the risk of hyperbole,” Mr. Sondheim later recalled, “I’d say that in that afternoon I learned more about songwriting and the musical theater than most people learn in a lifetime.”

In 1950 Mr. Sondheim graduated magna cum laude from Williams College in Massachusetts and moved back to New York, where he studied with the modernist composer Milton Babbitt.

Mr. Sondheim’s first musical was called “Saturday Night” (1954) but it would not be produced until 1997. By then he had come to know Laurents, who had been planning a modernized version of the “Romeo and Juliet” tale for the better part of a decade with Bernstein.

Choreographer Jerome Robbins had recently joined the team and it had been decided that Bernstein’s lyrics were not on a level with his music. Laurents remembered Mr. Sondheim from a tryout for “Saturday Night” and suggested a meeting.

“I left with mixed feelings,” Mr. Sondheim recalled in 2010. “I wanted to be asked to the party; I just didn’t want to go. The fact was, and still is, that I enjoy writing music much more than lyrics and even though ‘Saturday Night’ seemed as if it were dead in the water, I was planning other projects. I had the good sense to discuss all this with Oscar and it was he who persuaded me that if I was offered the job, I should leap at it. … Here was a chance to work with three of the most gifted and experienced men in music and theater. My desire to compose could be satisfied at any time.”

“West Side Story,” which opened in Washington, in August 1957, proved a radical and life-changing project for the young man, although Mr. Sondheim would always be embarrassed by some of his lyrics, particularly those for “I Feel Pretty.”

“I had this uneducated Puerto Rican girl singing ‘It’s alarming how charming I feel,’ ” he said. “You know, she would not have been unwelcome in Noel Coward’s living room,” referring to the prolific British wit and author.

It would take five more years before Mr. Sondheim wrote both music and lyrics for a show: “A Funny Thing Happened on the Way to the Forum,” a vaudevillian-style comedy starring Zero Mostel and based on the ancient Roman farces of Plautus. It was a critical and commercial success and ran on Broadway for two years before being turned into a film, also with the irrepressible Mostel.

“Anyone Can Whistle” (1964), which followed and featured a book by Laurents, was a spectacular flop, although it has won many admirers in the years since it closed on Broadway after only nine performances. It starred Angela Lansbury as the mayor of a decrepit small town.

In 1970, with “Company,” Mr. Sondheim began an 11-year partnership with the producer and director Harold Prince, one that lasted until the flop “Merrily We Roll Along”; they would reunite for “Bounce” in 2003, which never reached Broadway.

From 1984 to 1994, Mr. Sondheim’s most significant collaborator was Lapine, who pushed him increasingly toward the avant-garde. He preferred working with people he knew; Lansbury, Bernadette Peters, Lee Remick and Len Cariou were among his favorite actors, and he favored the orchestrator Jonathan Tunick for most of his career. (Mr. Sondheim composed for voice and piano.)

Although he was an erudite conversationalist, Mr. Sondheim regularly insisted that he much preferred puzzles of all sorts to reading books. “The walls of the lower level of his home are covered with 19th-century game boards,” Zadan reported in his book “Sondheim & Company.” “About the house are such artifacts as a skittle-pool table, obscure puzzles, a slot machine, jackpot games of various sizes, a gigantic chess set, antique ninepins, a ship’s telegraph, a glass harmonica (an 1820s set of tuned glasses) and a bicycle (Sondheim’s favorite form of transportation).”

Mr. Sondheim was an enthusiastic drinker for most of his life. “Unfortunately, I had, and still have, a great capacity for liquor, which is not good for the health,” he admitted. In his youth, he was also a heavy smoker but quit after suffering a heart attack at 49.

In addition to his theater work, he wrote a film with his friend, actor Anthony Perkins. Entitled “The Last of Sheila” (1973), the complicated mystery starred James Coburn and Richard Benjamin and was neither a critical nor a popular success.

Mr. Sondheim also wrote the soundtrack for Alain Resnais’s film “Stavisky” (1974) and five songs for Warren Beatty’s “Dick Tracy” (1990) one of which, “Sooner or Later (I Always Get My Man),” won him an Academy Award for best original song.

In 2010, Alfred A. Knopf published Mr. Sondheim’s “Finishing the Hat: Collected Lyrics (1954-1981) with Attendant Comments, Principles, Heresies, Grudges, Whines and Anecdotes.” The title comes from a song in “Sunday in the Park With George,” and the volume includes much valuable and illustrative self-criticism of Mr. Sondheim’s work, as well as frank and sometimes withering assessments of his creative forbears (W.S. Gilbert and Coward come in for particularly harsh treatment).

“Performing acts of literary self-criticism can be a tricky business, akin to being one’s own dentist,” Paul Simon, who has himself been writing distinguished songs for half a century, observed in a review for the New York Times. “After reading ‘Finishing the Hat,’ I felt as if I had taken a master class in how to write a musical. A class given by the theater’s finest living songwriter.”

Like many gay men of his era, Mr. Sondheim was guarded about his sexuality and reportedly lived alone until he was in his 60s. In 2017, he married Jeffrey Romley, who survives him. Information on additional survivors was not immediately available.

Despite his prodigious production, Mr. Sondheim always referred to himself as a lazy writer who was “usually dragged in kicking and screaming” into a project and then procrastinated until deadline pressure forced a creative spark.

For Sondheim – and his grateful listeners – the process was inevitably worth it. As he wrote in “Finishing the Hat”: “To be part of a collaboration is to be part of a family and for me – the only child of constantly working and mostly absent parents, a kid who grew up without any sense of family – every new show provides me with one. It may be a temporary family, but it always gives me a solid sense of belonging to something outside of myself.”

Tim Page, a former Washington Post music critic, is a professor of journalism and music at the University of Southern California.