“Television is really good at protecting the franchise,” Gilligan said. “It’s good at keeping the Korean War going for 11 seasons, like ‘M*A*S*H.’ It’s good at keeping Marshal Dillon policing his little town for 20 years. By their very nature TV shows are open-ended. So I thought, Wouldn’t it be interesting to have a show that takes the protagonist and transforms him into the antagonist?”

That was the pitch to AMC executives in 2007. The network was searching for a second original series, to go along with “Mad Men,” which made its debut that year. The goal was to find something set in the present, so that AMC wasn’t pigeonholed as the home of period television. And management wanted a conceit that would skew male and complement the network’s library of antihero action movies, the kind that star Clint Eastwood and Charles Bronson. Sitting in his Manhattan office, Charlie Collier, the president of AMC, recalls his introduction to Gilligan’s work: “Our development team put the pilot script on my desk and said, ‘Just read this.’ ”

At the time that Gilligan conceived “Breaking Bad,” his past success, plus all the hackwork offers that could have kept him busy for years, fortified his sense that only a show built to his iconoclastic sensibility was worth doing. He wanted a show devoid of snappy banter (of the kind that Aaron Sorkin writes), and one that doesn’t flatter you for getting its winking references (as Matthew Weiner does in “Mad Men,” with his chain-smoking doctors and kids playing with dry-cleaning bags). And he wanted a leading man who would not only change over the course of the series but also suffer crushing reversals with lasting impact.

That is something new. The depravities of leading men in TV dramas traditionally don’t leave permanent scars. Don Draper of “Mad Men” is still pretty much the tippling rake he has been from the start, despite a flirtation or two with confession and reform. Tony Soprano tried, through therapy, to improve as a human being, but he didn’t get very far. Dr. House of “House” will always be a brilliant cuss. Walter White progresses from unassuming savant to opportunistic gangster — and as he does so, the show dares you to excuse him, or find a moral line that you deem a point of no return.

In 2007, if you needed an actor to dramatize so profound a transformation, Bryan Cranston would have seemed an unlikely choice. Before “Breaking Bad,” he was known as the dad in “Malcolm in the Middle,” a broadly comic role. When Gilligan told AMC executives that he wanted Cranston to play Walter, they initially were baffled. Then Gilligan explained that years earlier, he cast Cranston in an episode of “The X-Files.” “We had this villain, and we needed the audience to feel bad for him when he died,” Gilligan said. “Bryan alone was the only actor who could do that, who could pull off that trick. And it is a trick. I have no idea how he does it.”

Meeting Bryan Cranston only deepens the mystery. He is Walter’s opposite. The character is coiled and burdened, while Cranston in person is buoyant. Walter’s default facial expression is a rictus of angst, while Cranston’s is a mischievous smile. Cranston looks at least five years younger than the character, and his co-stars say, he often behaves like a 10-year-old. Aaron Paul described Cranston as “a kid trapped in a man’s body.” Anna Gunn, who plays Skyler, Walter’s wife, says that she has never seen an adult more amused by stuffing fruit down his pants. But Cranston’s performance as Walter White has made history, winning three Emmys in a row for outstanding lead in a drama series, the first actor to do so since Bill Cosby in “I Spy” in the mid-’60s.

“Physically, to create Walter White, I use my dad,” he said one night over dinner. “My dad is 87 years old. I’m not going to dodder, but Walter is always a little hunched over, never erect. The message to the audience is that the weight of the world is on this man’s shoulders.”