Liberman, who had Parkinson's disease, died of pneumonia Sunday at Providence Tarzana Medical Center, said his daughter, Kay Liberman.
A former publicist for Warner Bros., Liberman launched his own public relations company, Frank Liberman and Associates, in 1947.
Over the decades, he handled dozens of top names, including Henry Fonda, Nat "King" Cole, Tony Bennett, Jack Paar, Harry Belafonte, Steve Allen, David Janssen, Charles Bronson, Joan Blondell, Dorothy Lamour, Joey Bishop, William Shatner, Mike Nichols and the songwriting team of Jay Livingston and Ray Evans.
As a publicist, Liberman was best known for his long relationships with Hope (41 years) and Diller (33 years).
In having Liberman as her publicist, Diller was following the lead of Hope, her comedic patron saint.
"That's the way I got Frank, because I pretty much did everything Hope did -- I tried to copy him," Diller, 92, said Wednesday with her trademark laugh. "I thought if it works for him, maybe it'll work for me."
Diller described Liberman as a "gentle man" with a "marvelous sense of humor. Frank was such a fun, fun, fun, fun guy. We were always back and forth with the jokes."
Publicist Dale Olson, who knew Liberman for about 45 years, said that "he became so identified with Bob Hope that he almost became Bob Hope, in that he was one of the greatest jokesters of the public relations profession.
"He was [delivering] caustic jokes all the time, and I think he got that from working with Hope's writers," Olson said. "I'm sure that's why Hope kept him on for all those years, because they joked together and Frank would respond to jokes. "He was so quick-witted and so good at jokes that he probably became the perfect audience for Bob Hope."
Indeed, when a Times reporter raised the issue of Hope's vast real estate holdings in 2003, Liberman quipped: "Bob and I have a lot in common. He owned the Valley, and I used to drive through it."
As a publicist, Liberman represented movies such as "The Miracle Worker," "David and Lisa," "Fiddler on the Roof," "Yours, Mine and Ours" and "Boy, Did I Get a Wrong Number."
He also publicized books, including biographies of Ethel Merman, Mae West and Gig Young -- as well as four of George Burns' books, four of Diller's and five of Hope's.
Born May 29, 1917, in New York City, Liberman grew up in White Plains, N.Y. and attended Cheshire Academy in Cheshire, Conn.
After graduating from Lafayette College in Easton, Pa., in 1938, he worked as a copy boy for the New York Daily News for a year before joining the Warner Bros. office in New York as a messenger. He was soon promoted to the press-books department and transferred to the Warner Bros. Chicago office as a "field exploitation man."
After serving as an Army public relations officer from 1941 to 1946, Liberman rejoined Warner Bros., where he worked as a unit publicist before establishing his own office.
Liberman was married for 31 years to Pat Harris, a former New York talent agent and a West Coast casting director, who died in 1984.
In addition to his daughter Kay, Liberman is survived by another daughter, Meg; and two grandchildren.
A memorial service is pending.
Instead of flowers, donations may be made to the Los Angeles Jewish Home for the Aging in Reseda or Project Angel Food in Los Angeles.