Paul Sills, one of the founders of the improvisational comedy group the Second City, which hatched some of America’s best-known comedians, died Monday. He was 80.

Sills helped found the comedy institution in 1959, along with its precursor, the Compass Players. Second City helped launch the careers of John Belushi, Bill Murray, Gilda Radner, Mike Myers, and Stephen Colbert.

“Somehow he ended up making the careers of dozens and hundreds of other people,” the author of “Something Wonderful Right Away: An Oral History of The Second City and The Compass Players,” Jeffrey Sweet, said. “Not a year has gone by that somebody coming out of [Second City] hasn’t achieved major stardom.”

Even though Sills was not looking for commercial or financial success, Mr. Sweet said, he found both at Second City. The group celebrates its 50th anniversary next year with stages in Chicago, Cleveland, Detroit, Las Vegas, and Canada, and has a reputation for training actors who go on to NBC’s “Saturday Night Live” and Hollywood.

“I don’t think he even particularly wanted it to happen,” Mr. Sweet said. “He was never interested in product. He was always interested in the journey.”

Sills was inspired by his late mother, Viola Spolin, who created hundreds of improvisational games used to train generations of actors. Sills followed in her footsteps and was known as a guru of improvisation.

He also created the New Actors Workshop in New York in 1987, along with director Mike Nichols and colleague George Morrison.

Sills also is known for creating the popular Story Theatre format in the late 1960s and early 1970s, which focused on characters narrating their own stories. His play, “Story Theatre,” was nominated for a Tony Award in 1971.