Breaking Bad creator Vince Gilligan cast Bryan Cranston for the role of Walter White based on having worked with him in the "Drive" episode of the science fiction television series The X-Files, on which Gilligan worked as a writer. Cranston played an anti-Semite with a terminal illness who took series co-protagonist Fox Mulder (David Duchovny) hostage. Gilligan said the character had to be simultaneously loathsome and sympathetic, and that "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."[43][45] AMC officials, who were initially reluctant with the casting choice, having known Cranston only as the over-the-top character Hal on the comedy series Malcolm in the Middle, approached actors John Cusack and Matthew Broderick about the role.[46] When both actors declined, the executives were persuaded to cast Cranston after seeing his X-Files episode.[47]
Cranston contributed significantly to the formation and development of the Walter White persona. When Gilligan left much of Walter's past unexplained during the development of the series, the actor wrote his own backstory for the character.[43] At the start of the show, Cranston gained 10 pounds to reflect the character's personal decline, and had the natural red highlights of his hair dyed brown. He collaborated with costume designer Kathleen Detoro on a wardrobe of mostly neutral green and brown colors to make the character bland and unremarkable, and worked with makeup artist Frieda Valenzuela to create a mustache he described as "impotent" and like a "dead caterpillar".[48] Cranston repeatedly identified elements in certain scripts where he disagreed with how the character was handled,[49] and went so far as to call Gilligan directly when he could not work out disagreements with the episode's screenwriters. Cranston has said he was inspired partially by his elderly father for how Walter carries himself physically, which he described as "a little hunched over, never erect, [as if] the weight of the world is on this man's shoulders". In contrast to his character, Cranston has been described as extremely playful on set, with Aaron Paul describing him as "a kid trapped in a man's body".[43]
Aaron Paul's casting was also initially questioned by production, as Paul looked too old and too much of a "pretty boy" to be associated with meth cooking. Gilligan reconsidered Paul's skills after seeing his audition and recalling he had also had guest starred on The X-Files episode "Lord of the Flies".[28] Gilligan originally intended for Pinkman to be killed at the end of Breaking Bad's first season in a botched drug deal as a plot device to plague Walter White with guilt. However, Gilligan said by the second episode of the season, he was so impressed with Paul's performance that "it became pretty clear early on that that would be a huge, colossal mistake, to kill off Jesse".[50] Similarly, Dean Norris had shown his ability to be a law enforcement official in The X-Files episode "F. Emasculata", and was brought on to be Hank Schrader, Walter's brother-in-law and DEA agent.[51]