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. 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". Cranston repeatedly identified elements in certain scripts where he disagreed with how the character was handled, 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".