The new documentary Ask Dr. Ruth doesn’t ask you to put aside everything you think you know about sex therapist Ruth Westheimer, since her public persona isn’t too far from the truth. But director Ryan White (The Case Against 8) does need you to push your assumptions to one side and make room on your Dr. Ruth shelf for a whole lot you had no idea about.

And if you’re one of those people who have long dismissed Dr. Ruth as something of a joke — well, I can’t say “shame on you,” since shame is an emotion the good doctor rejects, but at least pay attention.

Westheimer is something of an amalgam of the two roughly contemporary cultural icons enshrined in equally excellent documentaries in 2018. As a woman, she’s a pioneer in her field, fighting for feminist values (with a supportive husband) like Ruth Bader Ginsburg of RBG. And as an entertainer, she wrapped serious topics into a popularly accessible broadcast package, like Fred Rogers of Won’t You Be My Neighbor?

Ask Dr. Ruth won’t have quite the emotional undertow of those docs, since viewers are unlikely to have the personal investment common with Justice Ginsburg and Mr. Rogers, even if they recall Westheimer at her peak in the 1980s and 1990s — talking sex on her ubiquitous radio and TV programs, or appearing as a guest on other chat shows. But the film is nonetheless powerful in its own way, particularly recounting Westheimer’s escape from the Holocaust, which wiped out her family.

In addition to a surprising number of period photographs, the filmmakers have created some lovely computer animation (in a hand-drawn, watercolor style) to dramatize moments in Westheimer’s past, and the segments are quite effective. An ample number of spot-on interviews with friends, family and associates from more recent decades fill out the picture.

But of course the star throughout is the fearless, funny Dr. Ruth herself, whether in the footage shot for the film around her 90th birthday on 2018, or in archival clips. Every time some desperate voice from the past poses one of those now-familiar wince-inducing sex questions, you’ll want to hear Dr. Ruth’s perky, informed, shame-free answer. (Sometimes you do hear it, sometimes you don’t.)

As Ask Dr. Ruth makes clear, there has never been anyone quite like Dr. Ruth Westheimer and isn’t likely to be again.

Grade: A-minus. Opens May 3 at the Fine Arts Theatre.

(Photos: Magnolia Pictures/Hulu)