Disclaimer of a movie: Can it really save the producers?

The New York Times asked that question about Mark Zuckerberg and the movie The Social Network:

... how can filmmakers take liberties with the story of a living person, and does that person have any recourse if the portrayal upsets him? After all, many movies run a legal disclaimer in the credits that says, “Any resemblance to real persons, living or dead, is purely coincidental.”

[...]

When it comes to public figures, lawyers say, appropriating someone’s life story for a movie is not so different from telling such details in a news article or printed biography.

• Floyd Abrams, a leading First Amendment lawyer, says “a moviemaker is not going to get less protection than a journalist. If they’ve got sources and depositions and the like, and they use it in a reasonably fair way, they are likely protected.”

• Eugene Volokh, a professor at the University of California, Los Angeles, law school, said that if Mr. Zuckerberg sued and was declared a public figure, he would then “have to show that the filmmakers knew the statements were false, or were reckless about the possibility of falsehood.”

Screenwriter John August puts it this way for non-public figures:

Let’s say the movie has an evil drug dealer named Joe Thompson. If some guy named Joe Thompson in Wayzata, Minnesota decides the movie has defamed him and tries to sue, the studio can point to that disclaimer and say, "Look, we said this character wasn’t based on anyone."

From Stanford University - What Good Are Disclaimers?:

When using a person’s name or image, some businesses attempt to avoid liability for breaching a person’s publicity or privacy rights by providing a disclaimer.

[...]

A disclaimer by itself will never shield a business from liability.

Note: This is about disclaimers in general, not just in movies.

The Hollywood Reporter made a list of the Top 10 legal disclaimers in Hollywood History:

• "This production has not been approved, endorsed or authorized by the Federal Bureau of Investigation." -- The X-Files

• "All characters and events in this show —even those based on real people— are entirely fictional. All celebrity voices are impersonated ... poorly" -- South Park

  ^{[click the link above for the full list]}

It is certainly possible to sue internationally, but I feel like the details about that subject are out of scope for Movies.SE.

First of all, let me say this: do not take this answer as legal advice. I'm not a lawyer.

Let's analyze it a little bit. If you make a movie with that disclaimer and someone sues you, what's likely going to happen in court?

Now, it's true that things (especially legal things) change from country to country, and they change a great deal sometimes, but I think it's safe to assume that your lawyer could use this to help your case in court.
If the president in your movie is corrupted, you're not necessarily saying that the real one is too. You just want to preserve your freedom of creation, by saying "in my movie/story the president is corrupted", that's all. A movie should not be constrained by real world issues up to that point. Sure, there are some limits but those usually coincide with balance and common sense. Some TV series use this disclaimer, such as Cold Case or Law & Order. Unfortunately this is not what is always going to happen, and this is why if you're considering writing a book or making a movie, you should always make sure that the characters are unique enough, not only as characters per se, but also different from real life people that might consider themselves defamed by your work.

And if your movie is about a John Smith that robs a bank in New York, and you don't use the disclaimer, it's very likely every single John Smith will sue you for that. Using the disclaimer will improve your chances of avoiding lawsuits from every John Smith in the city.

But, there's a but.

However, if the two entities (real person and character) share too many things that might have them associated, then the director/creator might face legal consequences.

Creating a character and changing the name might not be enough, as there are many things that could help people associate two people that share other details: social background, ethnicity, particular episodes, appearance, job, etc. If someone knows the person you took inspiration from and, basing on details in the book, they can identify that person in that character you can end up being in trouble.

This is why the disclaimer is useful but doesn't make anyone invincible. And it should be clear that the disclaimer doesn't deny people from suing you. It can definitely happen, but it can be useful both before lawsuits (people won't care, after all, you said all characters are fictional), and during lawsuits. Yes, it should be used because it helps, but only meaning that it might help you in case of lawsuits, not that people will be 100% prevented from suing you.

You can read a bit more about it in its relevant Wikipedia page. To reiterate, the page states that it

is done to reduce the possibility of legal action for libel from any person who believes that he or she has been libeled via their portrayal in the work (whether portrayed under their real name or a different name)

however, very important (emphasis mine)

The wording of this disclaimer differs from jurisdiction to jurisdiction, and from country to country, as does its legal effectiveness.

As a lawsuit filed against Dick Wolf shows, we can see that such a disclaimer won't protect you and won't deny people from suing you if they deem it necessary.

William Alchesay (May 17, 1853 - August 6 1928) was a prominent White Mountain Apache chief, who lived to be 75 years old according to his strangely precise birth date.

Suppose that he lived twenty or more years longer, until Fort Apache premiered in 1948 and until he or a relative saw the movie. He might have decided to sue the producers for depicting him as a hostile leader who helps massacre the US cavalry I can picture him being brought into the court on a wheelchair wearing his medal of honor earned in 1872-73 to testify.

Suppose that long-dead people, or their heirs, could sue for defamation of character. If you watch a lot of cavalry and Indians movies you will notice that a lot of real persons, red and white, could have sued the producers for defamation of character if the dead could sue.

For example, Colonel Thursday in Fort Apache is based on a fictional character in a story by James Warner Bellah who is obviously based on George Armstrong Custer. Fort Apache is often described as a fictional version of Custer's Last stand. If the dead or their heirs could sue, the legal question would be whether the obvious similarities between Thursday and Custer constituted defamation of Custer's character.

In The Glory Guys (1965) General Frederick McCabe seems even more obviously based on Custer, since the enemies are Sitting Bull's Sioux, McCabe attacks them without waiting for General Hoffman's forces, and the Battle of Fishbone Creek seems based on the Battle of the Washita.

The dead and their heirs can't sue for defamation of character, but if a fictional character is based, just as obviously as in those examples, on a living person, that living person would have a chance to win a lawsuit against the producers.

So no doubt in various jurisdictions there are legal precedents about how much a fictional character can resemble a living person and cause people to think that the character is obviously that living person under a pseudonym without the living person having a right to sue.