All baby boomers worth their salt remember bathing with Dr. Bronner’s Castille Soap. And shampooing with it. And brushing their teeth with it, too. More fun than the soap’s peppermint tingle was reading the label, which detailed the impenetrably abstruse philosophy of Dr. Bronner and, perhaps, exposed him as a bit of a kook.

He was that, and much more, as shown in a new documentary “Dr. Bronner’s Magic Soapbox.” The film recounts not only Emil Bronner’s amazing business success, it also explores the intergenerational relationships of the Bronner family.

In fact, for all the clips of Dr. Bronner spouting off, his peripatetic son Ralph, heir to the Bronner soap business and tireless promoter of his father’s legacy, emerges as the true star of the film.

“Dr. Bronner’s Magic Soapbox” will screen at the Mill Valley Film Festival on Oct. 10 and 11.

“Dr. Bronner’s Magic Soapbox” attempts to do more than string film clips and talking head interviews, though it has those. There’s whimsy aplenty, with soap-lover-on-the-street interviews superimposed on a Bronner label, sing-along song lyrics (presumably written by Bronner), and ample footage of Ralph Bronner trolling the streets of New York, hawking soap and giving out hugs to passersby.

That Ralph would be a touch eccentric is no surprise given his bloodline. His father, Emil Bronner, was born in 1908, the son of an Orthodox Jewish soapmaker in Heilbronn, Germany. He came to America in the 1930s and tried his hand at making soap from an old Castillian recipe (hence Castille soap). At the same time, Bronner developed his All-One-God-Faith philosophy, a pan-religious hodgepodge loosely derived from the Sh’ma, the Jewish prayer which Bronner himself recites in one clip.

The film also chronicles Bronner’s incarceration in a mental hospital and his subsequent escape to California, where he built his soap-and-philosophy business into a multi-million-dollar success.

Bronner comes off as a tough old bird, dedicated to fair treatment of his employees, natural living and spreading the gospel of All-One-God-Faith. Scenes of him dictating new quotes for soap labels, spoken in that odd syntax of his, are fascinating.

But he was a far from perfect man. Bronner abandoned his three children to a series of Dickensian orphanages and foster homes. He clearly favored his youngest son, Jim, who eventually ran the soap business and died fairly young. Jim Bronner says in one archival clip that he didn’t even know he was half-Jewish until adulthood.

Today Bronner’s grandsons, who proudly claim their Jewish heritage, run the business while Ralph tours the country, a kind of Johnny Soapbottle. As he says, “The soap is an excuse to live a righteous life.”

As evidence, the Bronner family donates 70 percent of profits to charity, gives employees generous bonuses and is scrupulous about being an environmentally friendly enterprise.

While entertaining, “Dr. Bronner’s Magic Soapbox” runs out of gas about two-thirds of the way through. By then, it has said all it has to say about Bronner, his dysfunctional family and his heirs efforts to live righteous lives, yet it plods on repetitiously for another 20 minutes or so.

But there are arresting scenes all the way through, none more so than Ralph’s encounter with a scruffy New York musician living in a fleabag hotel while nursing his dying girlfriend. Ralph prompts him to play his piano, and when the musician’s lyrical improvisation brings tears to his eyes, Ralph gently prods the young man to express his feelings in words. It has nothing to do with soap, and everything to do with simple human contact.

The film reveals Bronner as a “member of the tribe” in good standing, but one who went off on a mercurial path. He is shown as an ardent Zionist (the blue and white soap bottle label is, ostensibly, a salute to Israel) and there is all that “God-is-One” stuff to seal the deal.

But above all Bronner and his heirs constitute a classic American success story. Here’s a guy who was once locked up in a mental hospital for spouting lunacies, and a few years later becomes a business and cultural icon for those very same lunacies. It’s enough to give you a peppermint tingle all over.

The Mill Valley Film Festival presents “Dr. Bronner’s Magic Soapbox,” 9:15 p.m. Tuesday, Oct. 10 at [email protected] Sequoia, 25 Throckmorton Ave., Mill Valley; and 9:15 p.m. Wednesday, Oct. 11, at the Christopher B. Smith Rafael Film Center, 1118 Fourth St., San Rafael. Tickets: $8-$10. Information: (925) 866-9559 or online at mvff.com.