Widely regarded as one of the best films ever made, Taxi Driver’s greatness is synonymous with the performance of Robert De Niro, who carried the film on his shoulders as disillusioned and insomnia-ridden Vietnam veteran Travis Bickle. We see the city of New York almost exclusively through his eyes, and, as the movie was filmed amidst both a heat wave and a garbage strike, it underscores the claustrophobic tension throughout, mounting with each scene until it eventually erupts in one of the most violent and controversial endings in film history.

As De Niro turns 72 today, we look at his substantial creative investment that he put into this iconic Oscar-nominated role.

He drove a cab for months in preparation for the role.

After eventually being offered the role by Martin Scorsese, De Niro was busy filming 1900 in Italy. However, every break from filming he’d get, he’d fly to New York and, having actually obtained his cab driver’s license, worked 12-hour shifts until returning to Italy to resume filming. Having already won an Oscar for his work on The Godfather Part II, he would occasionally be recognized. Stories include De Niro once telling a passenger, “Well, that’s acting. One year the Oscar, the next you’re driving a cab!”

While filming in Italy, he’d work on his Midwestern accent.

When not flying back to New York City to moonlight as a cab driver, he’d spend downtime in Italy listening to taped recordings of Arthur Bremer’s diary, the man who’d shot presidential candidate George Wallace in 1972, who is a noted influence for the character. He would also visit an army base in Northern Italy where he’d befriend a group of U.S. soldiers who were from the Midwest. De Niro studied their accents, their mannerisms, and way of dress, all of which became part of De Niro’s portrait of Bickle.

He improvised the diner scene with Jodie Foster dozens of times before filming.

As Travis slowly moves from drifting loner to self-aggrandized vigilante, he begins to develop a relationship with a 12-year-old prostitute named Iris, played by Jodie Foster. Prior to filming, De Niro would meet Foster, taking her to different diners around New York City, at first saying nothing, then eventually running down the scene with her over and over to the point where she called it “pretty boring because I already knew the lines.” Eventually, he would improvise ideas, making her follow him on tangent ideas within the confines of the scene itself. Foster would call the exercise “a huge revelation,” redefining her idea of what it meant to be an actor. 

The movie’s best-known line was improvised.

A great deal of the dialogue in Taxi Driver was improvised by the actors, the infamous “You talkin’ to me?” scene was written in the script simply as “Travis talks to himself in the mirror.” Playing the scene off like an angry kid with a toy gun, it’s the moment that Bickle becomes completely unhinged, with only his vendetta in mind. In his 2009 memoir, E Street Band saxophonist Clarence Clemons credited the line to something Springsteen had said on stage while De Niro was attending a concert, which he later admitted to him during their work together on New York, New York.

He’s still interested in revisiting the character.

Rumors of a sequel have been circulating for years, always seemingly at De Niro’s insistence. While Paul Schrader and Scorsese are both adamant that the ending is to imply Bickle will snap again, only this time “won’t be the hero,” with Schrader going so far as to say during a Reddit AMA that he envisioned the character dead less than six months after the movie’s end credits. Even though he agreed, De Niro admitted in an interview with the Guardian in 2013 that he’d “like to see where Travis is today. There was something about the guy – all that rage and alienation, that’s what the city can do to you.”