Stephen Sondheim, the towering figure of American theater whose works includes Company, A Funny Thing Happened on the Way to the Forum, Sunday in the Park with George, Sweeney Todd, Follies, Into the Woods, and Assassins and lyrics for West Side Story and Gypsy, died in his home in Connecticut on Friday, the NY Times reports.

He was 91, and his lawyer and friend Richard Pappas told the Times that his death seemed "sudden" and that Sondheim had celebrated Thanksgiving with friends.

The Times wrote in its extensive obituary, "An intellectually rigorous artist who perpetually sought new creative paths, Mr. Sondheim was the theater’s most revered and influential composer-lyricist of the last half of the 20th century, if not its most popular." Variety noted how he "slowly moved away from [Broadway's old] melodic tradition to incorporate complex and dissonant themes and structures of 20th century classical music into his works."

Sondheim was born in New York City and lived on the Upper West Side. His mother's friendship with Dorothy Hammerstein resulted in Sondheim befriending Hammerstein's son and, eventually, becoming mentored by her husband, the Broadway lyricist Oscar Hammerstein II, whose partnership with Richard Rodgers defined American musical theater in the middle of the 20th century. "While [his father] Herbert Sondheim introduced his son to music, it was Hammerstein who had a profound influence on the young composer," according to "'If he'd been a geologist,' Sondheim often stated, 'I would have been a geologist."'"

In September, Sondheim appeared on The Late Show With Stephen Colbert—with Colbert calling him "the greatest composer and lyricist in the history of American theater"—and reflected on what Hammerstein told him. "He told me to write for myself, because I wrote songs that imitated him. He said, 'No, write what you feel... This is what I feel about love and humanity. You write what you feel.'"

Sondheim also revealed to Colbert that he was still writing, working on a musical with David Ives called Square One, which he was hopeful would be ready next season.

He won eight Tony Awards for seven works (Company, Follies, A Little Night Music, Sweeney Todd, Into the Woods, and Passion) as well as a Tony Award for lifetime achievement; eight Grammy Awards; an Academy Award for "Sooner or Later (I Always Get My Man)," an original song in the movie Dick Tracy; and a Pulitzer Prize, with frequent creative collaborator James Lapine, for Sunday in the Park with George.

Earlier this month, he attended the openings of two revivals of his shows, Assassins at the Classic Stage and Company at the Bernard Jacobs Theater. Patti Lupone, another longtime collaborator, saluted Sondheim from the stage:

For Sondheim's 90th birthday last year, a who's who of Broadway (and Hollywood) stars performed a virtual concert.

For a great assessment of six Sondheim songs, stream Six by Sondheim on HBO Max.

When giving him the Presidential Medal of Freedom in 2015, President Barack Obama said, of Sondheim "As a composer and a lyricist, and a genre unto himself, Sondheim challenges his audiences. His greatest hits aren’t tunes you can hum, they’re reflections on roads we didn’t take and wishes gone wrong. Relationship so frayed and fractured, there’s nothing left to do but send in the clowns.”

Music critic Tim page, in his obituary of Sondheim for Washington Post, quoted from Sondheim's memoir 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."