Transforming DiCaprio into an aging Hoover took much more than just an extensive make-up process. Aside from learning to move more slowly, the actor studied the FBI director almost compulsively. DiCaprio said he traveled to Washington, D.C., where Hoover was born and lived with his mother until he was 40 years old, and visited the bedroom he died in. DiCaprio also walked the halls of the FBI building and sat in Hoover's chair, trying to get a feel for what it was like to be "The Boss."
DiCaprio and Eastwood also interviewed former FBI agents who worked under Hoover to find out how the FBI director would speak to people, how he would gesture -- even if he liked donuts -- to further develop his character for the film.
Former FBI agent Deek Delosh was one of the last agents to know Hoover well. According to DiCaprio, Delosh described Hoover as a man who became more sensitive and emotional as he got older.
"[Hoover] felt things fragmenting around him," DiCaprio said. "He felt his, sort of, power diminishing and his influence diminishing and he would oftentimes have bouts of depression where he would be sobbing."
But one of the more challenging scenes, DiCaprio said, was when he, portraying an older Hoover, had to sit across from Jeffery Donovan, who plays a young Robert Kennedy in the film.
"[Hoover] speaks to him like he's a young whippersnapper wet behind the ears and doesn't know the first thing about politics," DiCaprio said. "So to have not only the weight and all the prosthetics, but to have that sort of command at 50 years of experience under your belt and you know, knowing this country on a more intricate level than this young political upstart could ever imagine, was a challenging one."
DiCaprio recieved an Oscar nomination for his portrayal of Howard Hughes in the 2004 film, "The Aviator," but is still more recoginzed today for playing Jack Dawson in the 1997 blockbuster "Titanic," a role he said he was "very proud" of. He added that it is not the characters that draw him into doing a film, but the story.
"To do a movie just for the sake of doing a romantic comedy or doing a science fiction film seems sort of a profound waste of time," DiCaprio said. "You read something and if you're moved by it and you feel like you know it can be a perfect film and you can do a good job in it and that's sort of my philosophy."