Andrew Cooper Director Martin Scorsese sets up a shot with Leonardo DiCaprio as Howard Hughes in "The Aviator," a screenplay written by John Logan. Click photo for larger image.

Knowing that Leonardo DiCaprio will star in the movie you're writing is like handing a child a deluxe box of crayons -- the kind with 64 or even 96 colors.

"In the case of writing for Leo, it was incredibly liberating," says "The Aviator" screenwriter John Logan in a call from Los Angeles. "I had, even before I met him, such respect for his talent, I knew that I could write with the entire color spectrum, if you will. I could write a character who was dark, a character who was light, a character who was sexy, and he would be able to play all of those."

And Howard Hughes in "The Aviator" is all of those and then some.

"What surprised me the most about Howard Hughes was undoubtedly how lonely he was and how sad he was. He didn't have friends the way you and I have friends. He had employees and he had girlfriends that, with the exception of perhaps Kate Hepburn, Ava Gardner and maybe Ginger Rogers, he didn't treat as equals, so he was a very isolated and sad, sad man."

Logan, a playwright turned screenwriter, spent five years researching, writing and refining the script for the Martin Scorsese film, which opened here on Christmas. He spent a year doing research -- into Hughes, Hepburn, Old Hollywood, military and commercial aviation, the corporate histories of TWA and Pan Am and obsessive-compulsive disorder.

He ordered as many books as possible and retreated to the Chicago Public Library and Northwestern University library to pore over microfilm, microfiche, old newspapers and scandal magazines. Logan took copious notes and compiled a master chronology, a year-by-year description of Hughes' life complete with key events and relevant quotes. It ran 250 pages.

Aviation emerged as the project's natural spine. "A lot of the research began to organize around those blocks of the various planes. It was almost novelistic, with the various planes as chapter heads."

John Logan, who wrote the screenplay for "The Aviator," was a Chicago playwright before going on to write or co-write "The Last Samurai, "Star Trek: Nemesis," "Gladiator" and "Any Given Sunday." Click photo for larger image.

"The Aviator" concentrates on a slice of Hughes' life -- from the production of his movie "Hell's Angels" in the late 1920s to TWA's emergence as a major international airline in the late 1940s. Logan walked the delicate tightrope of serving both man and movie.

"I am not a historian. I am not a biographer. I'm a guy who wrote a movie. I'm a dramatist," says Logan, who worked closely with Scorsese and DiCaprio. "This is our perspective on Howard Hughes, this is our treatment of his life. ... What's always important to me is that, at the end of the day, we can feel we've been true to the spirit of who that man was, as we understand him."

The movie doesn't follow Hughes to the end of his days, when he died a recluse, wasted in body and mind.

"Since so much was foreshadowed of what his later life would be, it would be redundant to then dramatize it. The episodes he had, where obsessive-compulsive disorder became crippling for him, really began in his 20s and continued all through the period we dramatized."

In the film, we see Hughes as a germaphobe who compulsively washes his hands until they bleed and an OCD sufferer who clamps his palms over his mouth to stop himself from repeating a phrase. Logan says Hughes never sought help from a therapist for those problems because he had a fear of being institutionalized.

"What makes it so poignant for me is he's a man who knew he was mad and there was nothing he could do about it, and he lived in fear of being propped in a straitjacket and all his planes taken away and all his power taken away and just being rendered impotent within his own life. So while he sought out doctors to help with his hearing impairment and obviously the injuries he suffered in plane and car crashes, in terms of psychiatric help available, no, he made no use of that."

In fact, Logan calls the scenes where Hughes slides into mental illness the most harrowing writing he's done in 25 years. "The places Howard Hughes went to were hellish, they were very extreme and very difficult, and it was hard to write, it was hard to act, it was hard to direct. It was very challenging material."

Also daunting: writing dialogue for Hepburn, embodied here by Cate Blanchett. Moviegoers know how the real actress looked, moved and talked.

He gives the audience a rush of impressions of Hepburn in her first scene on a golf course.

"She talks a mile a minute and the synapses are jumping and the teeth are snapping, to prove to the audience, OK, there's Katharine Hepburn. There's the Katharine Hepburn you expect. We love her, she's maddening, she's magnificent, and now we can get beyond that, hopefully, into the character she is in Howard Hughes' story."

Logan, whose solo or shared writing credits include "The Last Samurai," "Star Trek: Nemesis," "Gladiator" and "Any Given Sunday," was a Chicago playwright before he tried his hand at movies. The stage served him well.

"All a playwright does is collaborate. You collaborate with the directors, actors, you're in rehearsals, you hear the play out loud, so segueing into movies was just a continuum of collaborating with other artists."

And, as his credits prove, he has a talent for making sweeping or sprawling material manageable. "I have a lot of experience with historical material. The 14 plays I wrote, nine or 10 of them are historically based. I just love history and I love research," and he does his own research, which enables him to almost internalize the material.

Asked his idea of the perfect biopic, he doesn't hesitate before responding "Lawrence of Arabia."

"I think that is just a magnificent presentation of that very difficult character's soul, and it's done so cinematically with such efficiency and while on one hand, it's an amazing, sweeping epic with the deserts and the battles but on the other hand, and more importantly, it really is about Peter O'Toole's face. It's about those eyes, and to me, that is the absolute paradigm of how to do something like this."

Logan, who recently moved from Chicago to Los Angeles, thinks there are echoes of Hughes the risk-taker and innovator in several notable figures today.

"Certainly I believe there are elements of Hughes in Ted Turner, in Richard Branson, in Harvey Weinstein -- people who are willing to gamble with their own money because they have a vision and some would say they're insane and some would say they're exalted, but they have nerve."