Ricky Gervais is a very funny guy. In The Office, the brilliant British sitcom he created and wrote with Stephen Merchant, Gervais played a cringingly hilarious office manager who was a lot less intelligent or talented than he believed. In Extras, also made with Merchant, he was just as good as a struggling actor who discovers the truth in the old adage of being careful about what you wish for.

Gervais has carried aspects of these personae onto the movie screen as well, in both small roles (For Your Consideration, the two Night at the Museum movies) and leading ones (as a miserable, mean-spirited dentist in Ghost Town).

With The Invention of Lying, Gervais takes his shtick into another inventive area. Co-written and co-directed by Gervais (with Matthew Robinson), The Invention of Lying sets up an alternative universe in which all people tell the truth at all times. It’s a world in which humans do not possess a “lying gene”, which eliminates such stuff as storytelling.

In this world, Pepsi signs read, “For when they don’t have Coke” and a nursing home is a “sad place where homeless old people come to die.”

Gervais plays a not-particularly-successful screenwriter named Mark Bellison — only in this world, the movies he writes are turgid historical documentaries that are merely read to the viewing audience by a snooty narrator named Nathan Goldfrappe (Christopher Guest in a smoking jacket). When he’s fired from his job, Mark’s secretary (Tina Fey) tells him she’s always “loathed” him, and when he goes out on a date with a hot neighbor (Jennifer Garner) he’s long had a crush on, she smilingly and pleasantly tells him she wouldn’t think of sleeping with a pudgy guy like him. At dinner, their waiter admits he took a sip from one of their drinks.

Unloved and out of work, Mark is about to be evicted from his drab apartment when a new idea flows through his brain — we actually see the brain synapses at work — and thus lying is invented.

What has already been a clever and funny movie then takes a clever, funny and philosophical turn. In addition to using lying to obtain money from banks and get rehired at his job, Mark tries to comfort his dying mother (Fionulla Flanagan) by telling her that a wonderful afterlife awaits her. Mark is overheard by hospital staffers and soon his story about what happens after we die makes him famous.

This all leads to a remarkable scene in which Mark, now beleaguered by thousands of people who want to know more, tells those assembled that there is a “Man in the Sky” who determines all that happens on earth. People greet this amazing news with excitement, confusion and lots of questions.

Although Gervais is clearly having some gentle, good-natured fun at the expense of religious belief based on faith, The Invention of Lying (originally entitled “This Side of the Truth”) wears its atheism lightly. Gervais’ humor raises questions but doesn’t preach. The story runs out of gas towards the end and succumbs to some predictable conventions of romantic comedy. But it never loses its intelligence, humor or heart.

The Special Features, particularly on the Blu-ray edition, are also very funny. The best is a six 1/2-minute scene that was originally in the film, entitled “Prequel: The Dawn of Lying”, which stars Gervais and many of the movie’s leading cast members (Rob Lowe, Jonah Hill, Jeffrey Tambor, Louis C.K.) as Paleolithic Neanderthals.

Lonely and scorned by the other cavemen, Gervais discovers lying after he is attacked by a wild boar, is saved when a boulder lands on top of the animal and then claims to the other cavemen and cavewomen that he vanquished the boar. Naturally, they believe him, and honor him.

Viewers will also get a lot of laughs out of “A Truly ‘Honest’ Making of Featurette with Ricky Gervais” and “More Laughter: Corpsing and Outtakes”. These include comments about Gervais by his cast and crew (Garner describes her costar’s laugh as sounding “like a sick hyena”) and an abundant supply of scenes which Gervais ruined by cracking up (or in the English parlance, corpsing) or making others burst out laughing.

“Ricky and Matt’s Video Podcasts”, another Blu-ray extra, feature Gervais taking the most mundane subject — such as leading viewers on a tour of his rented house in Massachusetts — and running with it. In fact, Gervais is so good at the medium that his British podcasts with Merchant and a friend, Karl Pilkington, are being turned into a new animated series for HBO, The Ricky Gervais Show, scheduled to debut in February.

And that’s no lie.