Stewart died Friday of natural causes at Cedars-Sinai Medical Center in Los Angeles, said a son, Sande.
He kick-started his career in 1956 when Monty Hall, then trying to break through as a game-show host, arranged for Stewart to meet with Mark Goodson of Goodson-Todman Productions, the company that came up with the prototype for the TV game show.
Goodson initially rejected Stewart's first idea, "Three of a Kind," which he described as a show featuring three contestants claiming to be the same person and a panel trying to ferret out the truth. When Goodson asked if he had anything else, Stewart mentioned "The Auctioneer," which was based on guessing the cost of consumer products.
On the spot, Goodson green-lighted the second pitch, which became the landmark game show "The Price Is Right." It made its debut on NBC in 1956 with Bill Cullen as host and moved to CBS in 1972 with Bob Barker as the longtime emcee. Drew Carey has been the host since 2007.
"Three of a Kind" became "To Tell The Truth," which also premiered in 1956, on CBS. Inspiration for the show had struck Stewart while he was on a crowded elevator wondering what everyone around him did for a living, Wostbrock said.
Around 1960, Stewart helped create a third hit for Goodson-Todman, "Password," which had its genesis in a brainstorming session, producer-director Ira Skutch wrote in his 1990 book "I Remember Television."
No one was certain who first suggested the concept for the show based on guessing words from one-word clues, according to Skutch, but Stewart's format made it work: Two teams of people competed using the same word, which was passed back and forth between teams until the word was identified.
"Password" was the first quiz show that paired "civilians" with celebrities, according to the "Encyclopedia of Television." With Allen Ludden as host, it was shown on all three major networks between 1961 and 1980. A prime-time version aired as recently as 2009.
In 1964, Stewart formed his own production company and had his greatest success with "The $10,000 Pyramid." It first appeared in 1973 and over time was packaged in increasing dollar amounts that crested with "The $100,000 Pyramid." A version simply called "Pyramid" left the air in 2004.
The "Pyramid" productions received nine Emmy Awards as best game show, according to Wostbrock.
Through his company, Stewart created 15 shows before retiring in 1991. They included such 1970s titles as "Three on a Match," "Jackpot," "Winning Streak" and "The Love Experts."
"It was not uncommon for Bob to have three or four game shows on every day," Wostbrock said. "With his success came big money, but the money never changed him. He wore sneakers. He wore jeans. He ate with the crew."
The son of a tailor, he was born Isidore Steinberg on Aug. 27, 1920, in Brooklyn to Jacob and Dora Steinberg, who had emigrated from Russia.
During World War II, Stewart served stateside in the Air Force. After his 1946 discharge, he enrolled in a radio-writing course. Within weeks the instructor hired him to work at a New York City radio station.
After losing an opportunity in television because he was Jewish, he changed his name to Bob Stewart, adopting the same last name a brother used, his son said.
When the production of "Pyramid" moved from New York to Los Angeles in 1982 to make it easier to book celebrities, Stewart also came west and lived in an apartment.
In the early 1940s, he married his high school sweetheart, Sara. She died at 67 in 1990.
Stewart is survived by three sons, Barry, Sande and David; two grandchildren; and two great-grandchildren.
Asked in 2008 how he would like to be remembered, Stewart — known for his wit and wordplay — responded: "Occasionally."