Story of diminutive sex therapist Dr. Ruth Westheimer on stage at New Rep in Watertown

Sex therapist Ruth Westheimer, better known as Dr. Ruth, a German-American with a voice once described as “a cross between Henry Kissinger and Minnie Mouse,” burst on to the public scene in 1980 with the radio show “Sexually Speaking.”

Before long, Dr. Ruth was hosting television specials and her own series for Lifetime. Her candor, humor and knowledge – coupled with frequent guest appearances on “The Tonight Show Starring Johnny Carson,” “Late Night with David Letterman,” and the game show “Hollywood Squares” – made her America’s go-to sex expert.

And while that’s how the now 90-year-old is best known, there is a lot more to her story, as playwright Mark St. Germain (“Freud’s Last Session”) details in “Becoming Dr. Ruth,” a one-woman show the New Repertory Theatre will present beginning April 27 at Watertown’s Mosesian Center for the Arts.

Actress Anne O’Sullivan will portray Westheimer in Watertown. It will be her fifth turn in the role originated by Debra Jo Rupp (“That '70s Show”) in two sold-out 2012 runs at the Barrington Stage Company in Pittsfield under the title “Dr. Ruth, All the Way,” and another at TheaterWorks Hartford.

O’Sullivan – Rupp’s understudy for the 2013–2014 off-Broadway run of “Becoming Dr. Ruth” at New York’s Westside Theatre – believes she knows the secret for the show’s success.

“Mark has written a deceptively simple look at an epic life,” O’Sullivan said recently by telephone from her home in Manhattan. “He has great gentility and he tells Dr. Ruth’s story very elegantly.”

St. Germain had a lot to work with while crafting the play, which he wrote with Westheimer’s consent and cooperation.

Born Karola Ruth Siegel on June 4, 1928, in Wiesenfeld, Germany, the only child of Orthodox Jews Irma and Julius Siegel, Westheimer was separated from her parents by the Nazis. Her mother and grandmother sent her to Switzerland to live in an orphanage as part of the Kindertransport.

By 1941, Westheimer had lost all contact with her parents, later learning they had died in the Holocaust. Emigrating at age 17 to British-controlled Mandatory Palestine, Westheimer joined the Haganah in Jerusalem, training as both a scout and a sniper. She moved to France in 1950 to study at the University of Paris, and, in 1956, immigrated to the U.S.

“I had no idea about her story,” acknowledges O’Sullivan. “I learned about her when I got this part. I feel deeply humbled when I play her now, so much so that I surrender my own ego to the grace of this woman. I do it for her and all the families that were devoured in the fires.”

One of the things the actress learned about Westheimer is that while she’s open to giving all manner of sex advice, she’s reticent to discuss her own life.

“I think of her as deeply admirable – someone who carries profound pain with great privacy. Even now, when more is known about her history, it is still hard to get her to talk about it.

“She’s not a mean person, but she can be stern. If someone approaches her with a question about her life, she’s likely to respond, ‘Please don’t ask me about that,’ ” says O’Sullivan.

The author of “Dr. Ruth’s Guide to Good Sex” and some 40 other books on sex and sexuality may not want to speak directly about her early years, but, according to O’Sullivan, she has become comfortable seeing her story on stage.

“As the understudy, I was there night after night off-Broadway and Dr. Ruth was there, too, at every performance. She may come to Watertown, too, because she loves to see the show and often brings family and friends with her.

“She’s adorable, and fiercely bright. She likes to talk on a very high level, but she also seems to have retained the original innocence she was born with,” explains O’Sullivan. “Along with that, though, she also has a fearlessness.”

O'Sullivan, born in Limerick, Ireland, has appeared in regional theaters, in films like “Speed” and “The Mirror Has Two Faces,” made television guest appearances on “Sex and the City” and three series in the “Law & Order” franchise, and was a regular on the short-lived Aaron Spelling prime-time soap opera “Models Inc.”

She has played both Emily Dickinson in “The Belle of Amherst” and Mary Harris Jones (aka “Mother Jones”) on stage, but Dr. Ruth is the first living real-life character she’s portrayed. It is not, however, the first time that she has imitated her unique speaking voice.

“I’ve always been good with accents, and I used to do her voice back in the ’80s just to entertain my friends,” recalls O’Sullivan. “To get ready to play her, though, I watched YouTube videos of her non-stop. She is in her ’60s in the play, so that’s the period I focused on.”

That period, of course, was when the diminutive Westheimer was at the height of her fame, exhorting her public to “Get some!”

“The sex stuff is great fun to play. Mark has brilliantly put it into the overall story of her life. The sex talk always creates a lot of laughter among audiences. The various ways that it’s worked into the play are just very, very funny,” says O’Sullivan.

'Becoming Dr. Ruth'

Presented by New Repertory Theatre

WHEN: April 27-May 19

WHERE: Mosesian Center for the Arts Mainstage Theater, 321 Arsenal St., Watertown

TICKETS: Start at $25

INFO: 617-923-8487; newrep.org