One’s tall, one’s short. One was raised in laid-back, perpetually sunny Hollywood, while the other grew up in New York City’s frenetic, shadowy Little Italy. One likes to dress down and sprinkle his surfer-dude patois with greetings like ”dawg” and ”homey.” The other wears anxiety on his crisply pressed sleeve, throws around vocabulary words like lachrymose, and talks faster than an auctioneer on his third double espresso.

So what on earth do 30-year-old movie star Leonardo DiCaprio and 62-year-old filmmaker Martin Scorsese see in each other? As it turns out, quite a lot. Leo has found in Marty a dependable guide who’s forever trying to make his movies better. Marty has found in Leo a surprisingly sensitive collaborator. ”Marty doesn’t go take walks in the park when he has time off,” says DiCaprio, with admiration and maybe a little pity in his voice. ”He goes into his screening room and watches a movie he’s seen 40 times to pick up another detail.” Scorsese says that in turn, ”I have kind of an affinity with Leo. We’re born in different times, different contexts, different worlds. But I can tell by certain films I’ve screened for him that he appreciated, there seems to be a similar base of emotions and psychological responses we tap into.”

They bonded on 2002’s Gangs of New York, a dream project for Scorsese that DiCaprio’s post-Titanic star clout helped get financed. Now Scorsese has ”bookended” the favor, he says, helping DiCaprio realize a long-standing ambition: to put on screen the improbable life of billionaire playboy Howard Hughes — or at least the saner part of that life. At a reported cost of $115 million, the star and director have together hand-tooled The Aviator, a nearly three-hour biopic that all but ignores Hughes’ sad final years, when he sequestered himself in his Vegas penthouse and became a virtual prisoner of his own paranoia, germ phobia, and obsessive-compulsive disorders — not to mention a raging drug problem fueled by multiple plane-crash injuries. According to DiCaprio, the 6-foot-4 Hughes at one point had ”like 20 needles broken off into his arm” (probably an exaggeration) and weighed about 90 pounds when he died.

Skipping the twilight-zone freak show, and thus avoiding having to show substance abuse that would almost certainly have turned a PG-13 picture into a hard R — a frequent Scorsese rating — The Aviator sets its course instead for Hughes’ happier middle age, packed with achievement and celebrities. It breezes through his adventures of the late 1920s through the late 1940s as a free-spending indie director and producer in Hollywood, his battles to turn fledgling airline TWA into a thriving commercial enterprise, and his up-down romance with actress Katharine Hepburn, impersonated boldly by Cate Blanchett right down to the slashing stride and the Bryn Mawr accent. The big concern for DiCaprio was whether audiences would like his interpretation of Hughes enough to ”be connected with the journey, and be behind him.” And since Aviator constitutes DiCaprio’s first star vehicle as an executive producer, the movie’s reception puts his taste as a project picker on the line as much as his box office pull. (Another issue: Low Aviator grosses could crimp his plans to work again with Scorsese this spring on The Departed, a remake of the Hong Kong flick Infernal Affairs.)