If you have watched a Broadway show from before you were born, you probably have Betty Corwin to thank.

The force of nature behind the Theater on Film and Tape Archive, who earned a special Tony Award for her efforts in 2001, died September 10 at the age of 98.

In the 1960s, Ms. Corwin— then a mother of three living in Connecticut—was working as a volunteer at Jacobi Hospital in the Bronx when she applied for a training program to become a social worker. To apply, Corwin had to write an autobiography.

“As I was writing the autobiography, I found myself thinking that the most exciting time of my life was when I worked in the theatre,” Corwin told Playbill in 2017. She had previously worked as a production assistant and script reader for producers on Broadway. Corwin never finished the autobiography. Instead of applying for the course, she reconnected with her old theatre contacts, determined to contribute to the industry in a meaningful way. Her sister-in-law Helen Harvey, a theatrical agent at the William Morris Agency, suggested to her one evening: “Why don’t you just tape and preserve Broadway shows? Everybody talks about it and nobody does anything about it.”

She immediately reached out to the New York Public Library for the Performing Arts at Lincoln Center. The response? “What makes you think you can do this?” Truthfully, Corwin didn’t know she could, but she wanted to try. It was enough for Thor Wood, head of the Theatre Division at NYPL at the time. He gave Corwin a desk, a telephone, and a three-month timeline to get her initiative off the ground. Corwin needed to get five unions on her side to move forward: Actors Equity Association, the Dramatists Guild, the Stage Directors and Choreographers Society (SDC), the union for stagehands and technicians (IATSE), and the union of professional musicians (Local 802).

The work of convincing the five unions was worthy of a play in itself, but she succeeded—spectacularly so. TOFT has continued to expand throughout the decades and, since its launch, now counts over 4,000 Broadway, Off-Broadway, and regional performances in its vault. Actors of all levels view past works to research a role, directors find inspiration, journalists discover context—all made possible by Corwin.

“We’ve really come a long way since the beginning,” said Corwin, who was honored in 2017 with a Special Lifetime Achievement Award from The League of Professional Theatre Women. In explaining her passion for preserving shows, Corwin hit on a universal truth for all theatrelovers: “I thought it was a sin that once these wonderful productions were gone that they were gone forever,” she said. “The terrific production of The Glass Menagerie with Laurette Taylor, or Marlon Brando in A Streetcar Named Desire—gone forever. That really troubled me.

Ms. Corwin was born in New York City on November 19, 1920. She is survived by her daughter, Pamela, sons John and Tom, three grandchildren, and two great-grandchildren.