BARBIE and Ken are beloved by millions of children - but the people behind the world's most popular dolls were involved in unsavory sexual behavior they kept secret for years, a new book reveals.

In "Toy Monster: The Big, Bad World of Mattel," out next month, Jerry Oppenheimer reveals that Jack Ryan, the Yale-educated designer who popularized Barbie, was a "full-blown seventies-style swinger" with "a manic need for sexual gratification."

Staging orgies at his Bel-Air mansion, Ryan, whose wives included Zsa Zsa Gabor, surrounded himself with busty Barbie clones, including Gwen Florea, who was the "voice of Barbie" in a line of talking dolls. The book quotes her: "He once said to me he loved me being tall so he could stick his nose in my boobs when he hugged me."

Ryan's friend, Stephen Gnass, confides to the author: "When Jack talked about creating Barbie . . . it was like listening to somebody talk about a sexual episode, almost like listening to a sexual pervert . . ." Ryan took calls at Mattel from a madam and patronized "high-class call girls to streetwalkers," including a "very thin and child-like" hooker. The book claims that Ryan "somehow rationalized that he was the only man in her life" until he was diagnosed with gonorrhea.

Barbie and Ken were named after the kids of Mattel founders Ruth and Elliot Handler - an honor that plagued Ken, who "grew up embarrassed and humiliated by having an anatomically incorrect boy doll named after him . . . [with] no hint of genitalia."

Despite marrying and having three kids, Ken was a closeted gay, Oppenheimer says. "To all those who knew him Ken Handler was a wonderful father, a loving husband . . . But there was another side to Ken. And in 1990 he was formally diagnosed with AIDS. His parents and wife were shocked." He died in 1994 in Greenwich Village, but obits didn't mention the disease.