De Niro actually got a cab license and drove around in a taxi to prep for the role. He also listened to tapes of would-be assassin Arthur Bremer's diaries, and visited a U.S. army base in northern Italy, using the accents of American Midwestern soldiers as the basis for Travis' accent.
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Martin Scorsese changed the race of Sport and the two other guys killed in the climactic rampage scene in order to avoid sending the wrong message. In Paul Schrader's original script they were all African-American.
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The tracking shot of carnage at the end took three weeks to prepare, since the filmmakers had to cut into the ceiling to carve a path to shoot it.
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John Hinckley Jr. who tried to assassinate President Reagan (and was declared "Not guilty by reason of insanity") was obsessed with Jodie Foster and tried to imitate Travis Bickle's attempt to kill Charles Palantine.
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De Niro improvised his famous "You talkin' to me?" line, but saxophonist Clarence Clemons said De Niro told him it was inspired by hearing Bruce Springsteen talk to a cheering audience.
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Steven Prince, who plays the gun dealer Easy Andy, was the basis for the heroin overdose and adrenaline injection scene in Pulp Fiction. He told the story about how he saved a girl from OD-ing by injecting her heart with adrenaline in the Scorsese documentary American Boy, about Prince's life.
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Harvey Keitel (who played Sport) said, "I worked with a pimp for a few weeks in creating the role of Sport. We wrote nearly all of the dialogue, me and this pimp. I recorded the improvisations we did. He'd play this pimp and I'd play the girl; I'd see the way he'd treat me, then I would play the pimp and he'd play the girl. We did that for a few weeks over at the Actors Studio."
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