TV Guide presents behind-the-scenes stories of each major character's casting process.

In the original draft of the pilot script, Walter White was celebrating his 40th birthday, not his 50th. The character was aged up, and Gilligan's top choice was Malcolm in the Middle alum Bryan Cranston. Gilligan knew Cranston from an episode of The X-Files he had written called "Drive," in which Cranston guest-starred as a villain who kidnaps Agent Mulder.

"He played a character who was really kind of a bastard, a real creep. Unpleasant, abrasive, downright dangerous," Gilligan recalls. "And yet, at the end of the hour, you as the viewer needed to feel... sadness, when his head blew up from the weird supernatural thing that was plaguing him."

AMC executives were understandably wary of the choice at first, knowing Cranston as the goofy dad Hal on Malcolm in the Middle. But after watching his X-Files episode, and seeing his turn in Little Miss Sunshine as the smarmy (and fittingly named) agent Stan Grossman, they were convinced. "I was like, 'Dude, if he can disappear in a role like that, he's an amazing actor,'" recalls Christina Wayne, then-SVP of scripted programming at AMC. "So, we called Vince and we were like, 'OK, you can hire Bryan Cranston.'"

Though the casting directors initially had four or five pages of actors who were considered or suggested for the role - including John Cusack, Matthew Broderick, Steve Zahn and Dylan Baker - Cranston was the only actor who received an official offer.

The character of Jesse Pinkman, Walter's former student turned meth-cooking partner, was also aged up. Originally, the character was supposed to be in his late teens, fresh out of high school. He was also supposed to die in the first season.

Executives also weren't sold on Aaron Paul right away - but for a very different reason than they were skeptical about Cranston. "Our thing at AMC was we didn't want anybody who was too good-looking in our shows," Christina Wayne recalls. "We wanted people to look like real people. I thought Aaron Paul maybe was too handsome. ... But then his audition came in and he was amazing."

The role of Walter's wife Skyler nearly bypassed Deadwood alum Anna Gunn entirely. The role had been narrowed down to a few actresses before Gunn, a favorite of the Bialy/Thomas casting agency, even came in. "[Casting director Sharon Bialy] had been wanting to get Anna in from the beginning but we kept getting a message back from her agent saying, 'She's sick, she's sick,'" casting director Sherry Thomas recalls. "Finally Sharon called her at home and said, 'I don't know what's going on with you, but this is the best thing I've ever read, and you need to look at this and you need to get your butt in here.' And she did. ... Sharon sent [her tape] over to Vince right away and he said, 'You're right. Get her in the mix.'"

Cranston had been cast at that point, and did chemistry reads with three other actresses as well as Gunn. "When you saw the two of them together," casting director Sherry Thomas says, "she held her own and gave him something to play off of. He wasn't driving the scene. She was... an equal in that regard." Cranston picked up on that as well. "Vince respectfully said, 'Do you have a favorite?'" casting director Sharon Bialy recalls. "And [Bryan] said, 'Who's your favorite?' I think we all responded 'Anna' and he said, 'That's mine, too.'"

Dean Norris was coming off a disappointing fall in which he was passed over for the lead in a pilot that he calls "one of the best scripts I ever read." But then he got the Breaking Bad script and was drawn to the role of Walter's brother-in-law, brash DEA Agent Hank Schrader. "It beat the other script. It was truly the best script I'd ever read," he says. And I was like, 'Oh, this can't happen again. This is my role.' I know I could nail this role and have fun with it."

The casting directors felt the same, with Sharon Bialy making the note that Norris "was born to play this role."

Betsy Brandt auditioned for both Skyler and Skyler's sister Marie, but was fixated on the latter role. "That was the role I was meant to have," Brandt recalls. "[Vince] kept saying, 'She needles her sister. She needles Skyler. She needles her. And I thought, god, that's fun to play."

The idea to make Marie an X-ray technician was also Brandt's. "When we were on the set, in the very early days of shooting the pilot... she sidled over to me and she said, 'What do you think Marie does for a living?'" Gilligan remembers. "And honestly, I hadn't given it a second's worth of thought. I had so many other things on my mind at that point. But I said, 'Uh, I don't know. What do you think?' And she just kind of pursed her lips and stared at the ceiling for a minute. Then she said, 'I think she's an X-ray technician.' I was like, 'What?!' I was so charmed by that, because it's so weirdly specific... I found that so wonderfully endearing."

Explains Brandt: "I just wanted to be as specific as I could be about her. ... I wanted her to be an X-ray technician or an insurance adjuster. I wanted her to have something to do with medicine but not be a doctor. Because I just felt like she had such a chip on her shoulder, and I wanted that to be able to come from some place."

In some respects, Brandt and Norris felt like their casting was fate, after they met and chatted in the waiting room as they prepared to go in and audition for Vince Gilligan. "I kind of felt like I knew this guy forever, even though I hadn't," Brandt says. "It was just easy for us to talk right off the bat."

Each recalls discussing how they were going to approach the roles.

"I was like, 'This is a comedy, right?'" Norris says. "I go, 'I'm not sure. It's funny to me.' She goes, 'Yeah, but they call it a drama.' I said, 'Alright. Well, whatever.'"

Brandt remembers the conversation a different way -- but the end result was the same.

"I said to him, 'I'm playing this as funny. This is funny, right?' And he went, 'Oh yeah. Yeah,'" Brandt says. "We both have always agreed afterwards that we both went in that day and brought a little more comedy to it than we would have had we not had that conversation."

Walter and Skyler's son, Walter Jr., was the last role to be cast and went to 13-year-old RJ Mitte. "I went in five times, four in Los Angeles and once in New Mexico, and I was actually the very last person to be cast," Mitte says. "I flew back to LA the same day, and I turned around and got on a flight the next morning to come back and start filming."

The character was based on a college friend of Gilligan's named Takehiko Kitazawa who suffered from cerebral palsy and passed away a few years after they left NYU. Gilligan and the casting directors were adamant about casting an actor who actually had CP. "I was thinking of [Kitazawa] and his family and all the things they must have gone through and that he went through," Gilligan says. "It was important to me to, if at all possible, hire someone who actually did have CP to play the part of someone with CP. It just felt like the right thing, in memory of Takehiko if nothing else."

For his part, Mitte appreciated the way Walter Jr.'s condition was handled on the show: "It was organic and it was something that was just part of the family," he says.

The youngest cast member by far, Mitte was schooled by a private tutor on set when he wasn't filming.

"He became a little heartthrob by the end," Sharon Bialy notes.