Bob Stewart, a television producer with a penchant for transforming the seemingly mundane into blockbuster game shows like “The Price Is Right” and “To Tell the Truth,” died Friday in Los Angeles. He was 91.

The cause was respiratory failure, his son Sande Stewart said.

Stewart’s long-running hit shows, which also included “Password” and the “Pyramid” franchise, relied on his belief that simplicity could fascinate viewers, Fred Wostbrock, a co-author of “The Encyclopedia of TV Game Shows,” said in an interview Monday.

As Stewart himself put it, in an interview for the Archive of American Television: “Once you cause somebody at home to talk to the set aloud, even by himself or herself, then you’ve got a good game show. You want them to say, ‘It’s number 2! It’s number 2! It’s number 2!’ before the moment of truth comes out.”

Stewart was standing in front of a store window in New York in 1955, listening to people wonder what a piece of furniture costs, when the idea for “The Price Is Right” popped into his head, he told Wostbrock.

In that show, which is still on the air for an hour each weekday on CBS, four contestants try to guess the price of an item — a boat, a refrigerator, the cost of house cleaning for a year. The contestant who comes the closest without exceeding the actual price wins.

Another of Stewart’s game shows had a similar genesis.

“Bob walks into a crowded elevator and thinks to himself, ‘What are their occupations? What does he do? What does she do? What are their stories?’” Wostbrock said. That was the start of “To Tell the Truth,” in which three people, all claiming to be the same person, try to befuddle a panel of four celebrities.

Those two shows began late in 1956, the year that Stewart joined Mark Goodson-Bill Todman Productions.

“The Price Is Right” made its debut as a daytime show on NBC. A year later NBC added a once-a-week nighttime version. The original version ran until 1965, the last two years on ABC. The original host was Bill Cullen. The show returned to the air in 1972 on CBS, with a new, livelier format. Bob Barker was the host of the new version until he retired in 2007, with Dennis James briefly hosting a nighttime version. Drew Carey has been the host since Barker’s retirement.