Jesse Eisenberg, left, and Joseph Mazzello are shown in a scene from “The Social Network.”

When it comes to making movies about real people, Hollywood has a long history of not letting the facts get in the way.

Nearly 70 years ago, there was “Citizen Kane,” chronicling the rise to power of media baron William Randolph Hearst. Now comes “The Social Network,” recounting the creation of Facebook by Mark Zuckerberg.

Although the two movies have a lot in common, both being wildly ambitious profiles of incredibly powerful but deeply flawed media visionaries, their stories feature an elemental difference that speaks volumes about the eras that spawned them. Though both films are a quasi-fictional telling of a real-life character’s story, they present the “truthiness” of their characters in radically different fashions.

When Orson Welles and Herman Mankiewicz wrote “Citizen Kane,” there was never any doubt that Hearst was the central character, even if his name wasn’t mentioned. After all, Mankiewicz knew him well, having spent many a night carousing at Hearst’s parties until he was banned for boozing it up too much. But in the time of “Citizen Kane,” fiction had a literary potency. And of course, when it came to a powerful czar like Hearst, fiction was a protective mechanism.

But times have changed. We live in an age when audiences demand reality, not a thinly veiled equivalent. So though a few films still fictionalize their subjects — the imperious fashion magazine editor in “The Devil Wears Prada” was clearly inspired by Anna Wintour — most movies these days give us the stories of real people, even if the stories don’t hew to the facts.

In the case of “The Social Network,” it’s not even clear what source material the movie is based upon. The filmmakers have said the movie was inspired by Ben Mezrich’s proposal for a book that was ultimately published under the somewhat breathless title “The Accidental Billionaire: The Founding of Facebook — A Tale of Sex, Money, Genius and Betrayal.”

To say that the book itself is not especially fact-based would be an understatement, since Mezrich acknowledges re-creating scenes, changing settings and even saying he used not just the factual record but “my best judgment.” (When Janet Maslin reviewed the book in the New York Times, she said it was “so clearly unreliable that there’s no mistaking it for a serious document.”)

To make matters foggier, “Social Network” screenwriter Aaron Sorkin has said that he didn’t really get a look at the book until his screenplay was nearly finished, having only listened to “Ben reading some notes off his computer.”

David Kirkpatrick, a veteran journalist who recently wrote a book with Zuckerberg’s cooperation titled “The Facebook Effect,” has called the movie “horrifically unfair.” Zuckerberg himself has labeled the film “fiction,” and, channeling Hearst, hasn’t allowed ads for “The Social Network” on Facebook. But it almost seems as if he thinks it would be uncool to further challenge the film’s version of events. So this all raises a number of questions:

Is “The Social Network” really about Zuckerberg? Or is he simply a fictional character Sorkin has decided to call Zuckerberg? And if so, should the audience, meaning all of us who will see the movie, feel a little uneasy about just how emotionally involved we should get in a story with an authenticity that has so many loose ends? After all, if it isn’t really Zuckerberg on-screen, whose life is it anyway?

In Hollywood, filmmakers are quick to argue that they are entitled to fictionalize people’s stories to their heart’s content as long as they do it in the right spirit. In other words: Trust us. When Sorkin was asked by New York magazine’s Mark Harris about scenes in “Social Network” that seem completely invented, he said, “I don’t want my fidelity to be to the truth; I want it to be to storytelling.”

This is sound screenwriting practice — the story always comes first. Though when Mankiewicz did it 70 years ago, at least he didn’t have his cake and eat it too. The modern dramatist largely gets to use real life as modeling clay, happily bending and twisting the character in ways that give the story its most appealing shape and heft. It’s obvious that “The Social Network” wouldn’t have remotely the same buzzworthiness if it were about a fictional social network pioneer named Matt Feinberg.