Is it actually legal to make movies about living people?

Having just watched Vice, the slightly wacky and far-from-flattering Oscar-nominated biopic about American politician Dick Cheney, I wondered whether filmmakers have to get permission to release a film about a real live person, and why Cheney would not want to sue over such an unflattering portrayal. I had the same thought after watching The Crown series, and other movies.
Well, apparently, the answer is no, no such permission is needed. It is absolutely legal to make a movie about a real live person (or a dead one), however fast and loose the movie may play with the facts. Technically, a person may have recourse to the courts under the laws of libel if they feel that a work of art is not factual and has thereby damaged their reputation. But the level of proof required may be high, and it is usually difficult to demonstrate damage to a reputation, and in practice the rights to freedom of speech usually win out over a person's rights to privacy.
The other consideration is the possible negative publicity of being seen to be trying to stifle the creativity of an artist. Going to the courts to protect one's privacy or reputation can also have the negative effect of just drawing more unwelcome attention, and may ultimately be counterproductive. This is often referred to as the Streisand Effect, after Barbra Streisand's 2003 legal attempts to suppress photographs of her private Malibu residence actually drew even greater public attention to it.