Inspired by the revelations about Harvey Weinstein, Louis C.K. and others, a total of nine women have come forward publicly for the first time to describe a pattern of sexual abuse and violations of trust by a man they considered a mentor and friend. Mr. Horovitz is an award-winning author of more than 70 plays, including “The Indian Wants the Bronx” (starring Al Pacino in 1968); “Park Your Car in Harvard Yard” (on Broadway in 1991); and “Out of the Mouths of Babes,” which ran Off Broadway last year.

Over his five-decade career, Mr. Horovitz has been an influential player in the theater world. As the founding artistic director of Gloucester Stage, a respected regional theater that called itself a “safe harbor for playwrights,” and as an Obie-winning writer whose work was produced frequently in New York and Paris, he has had the power to offer roles, jobs or a helping hand to generations of actors.

In response to questions this week, Mr. Horovitz, 78, told The New York Times that while he has “a different memory of some of these events, I apologize with all my heart to any woman who has ever felt compromised by my actions, and to my family and friends who have put their trust in me. To hear that I have caused pain is profoundly upsetting, as is the idea that I might have crossed a line with anyone who considered me a mentor.”

His son, Adam Horovitz, said in his own statement: “I believe the allegations against my father are true, and I stand behind the women that made them.”

Mr. Horovitz’s behavior around women had long been the subject of whispers. But since at least 1993, Gloucester Stage officials had known it was more than mere speculation: that year, Mr. Horovitz was the subject of an exposé in The Boston Phoenix in which 10 women accused him of sexual harassment and assault. The women’s names were not disclosed in the article. At the time the board’s president, Barry Weiner, dismissed the accusations and described some of the women speaking out against Mr. Horovitz as “tightly wound.”

Last week, the theater cut ties with Mr. Horovitz after learning of the accusations by Ms. Ermansons.

“I apologize to the brave women who came forward in 1992 and 1993 but were not listened to,” Elizabeth Neumeier, the Gloucester board’s current president, said in a statement. “We are individually and collectively appalled by the allegations, both old and new.”

A Mentor, Until He Wasn’t

The nine women who spoke with The Times described Mr. Horovitz as a complicated man who was, at times, a charismatic mentor and empathic friend. He taught at several universities and nurtured young writers, was generous with his wisdom and dazzled with tales of his famous friends. “He was very dynamic and a real creative force,” said Ms. Corman, the actress.