“Nothing is funnier than unhappiness,” Samuel Beckett wrote. “It’s the most comical thing in the world.” Lewis made bank on anguish. He’s the “Curb Your Enthusiasm” regular who makes creator Larry David appear, by comparison, exultant and balanced. At age 72, three days David’s senior (and born in the same Brooklyn hospital), Lewis is perpetually dialed to doomed, his innards worn on his sleeve. He is Le Miserable.

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But he might not be as miserable as he appears.

Lewis and David have known each other since age 12 at a summer camp in Cornwall-on-Hudson (on the grounds of New York Military Academy, attended by one Donald Trump. Lewis: “I pray I didn’t sleep in his bunk.”)

“We hated each other. He was an annoying, lanky, obnoxious basketball player,” Lewis says of David. Also, “I was a better shooter.”

David counters, “I was a better player. I had more moves. I was harder to guard.” Oh, and: “I could go left and right. And put up a jump shot. And I was a much better rebounder.”

At age 23, they met again doing stand-up in New York and became friends. “We’re as close as can be,” David says, though they rarely visit each other off-set. “We live too far apart,” David explains. About 23 miles. “We’re both extremely lazy when it comes to moving.”

The 10th season of HBO’s “Curb” has been exceptionally strong, even attracting Trump’s attention. In the premiere, David wore a “Make America Great Again” cap — as he put it, “a great people repellent” in liberal Los Angeles. Trump tweeted, “TOUGH GUYS FOR TRUMP!” with a video clip from the show. Lewis, a staunch Democrat, remains incredulous: “He thought it was praise!”

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When he signed on to “Curb,” Lewis insisted on a story arc of several episodes so he couldn’t be cut from the cast. He plays Richard Lewis, “the friend who really annoys Larry, and I really annoy him. Whenever I hit him with the truth — just straight-faced telling him the truth — he just starts laughing.” Their on-screen friendship, both insist, is a more contentious version of their real one.

“When you know someone that well, what makes it work is you can really say anything you want to a person like that,” David says. “Nothing is off-limits. We have so much trust in our friendship.”

A fixture on Letterman (48 times) and Howard Stern, Lewis is a recovering alcoholic (sheepishly, he admits, champagne was his favorite) and addict (cocaine, crystal meth) who has been sober since 1994. He has an eating disorder (body dysmorphia). He didn’t marry until his AARP years, age 57.

“I was really needy,” he confesses. Every utterance is a confession. “It was all about the road, and I came first.” His comic persona is that of the worst boyfriend you ever had back in your early 20s when you didn’t know better.

The plan was to interview him in person at his Hollywood Hills home. Instead, he will only chat on the phone, because of the pain, which is so very Richard Lewis.

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In conversation, he is mellow, gracious, a pussycat. Perhaps it’s age, success, “Curb” appeal or the din of his emotional pain quieted by physical discomfort. Then he offers, “I’m a very happy man.”

Really? Because there goes your career.

“No, I’m not a very happy man. I’m thrilled to be alive. I’m grateful for who’s in my life. I’ve got great friends, a great wife, a dog, and I have a great career, but . . . ”

There is always a but.

“But there’s just a part of me that’s always going to be never totally happy,” he says, “and I think that has a lot to do with my childhood.”

Note we are eight minutes into the conversation.

His father: “He was never home. He died before I was a comedian.” And his mother: “She had some emotional problems. She didn’t get me at all. I owe my career to my mother. I should have given her my agent’s commission.”

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Five therapists treated Lewis. “Some of them died,” he says. Lewis brought then-girlfriend Joyce Lapinsky to meet the last shrink, the one who lasted 18 years. The therapist’s suggestion: “This is as good as it gets.”

So, the marriage proposal in 2004. Lewis, in a T-shirt and boxer shorts, not looking at Lapinsky, who is reading: “I guess we have to.”

Lapinsky: “Yeah, okay.”

It’s possible that Lewis is, if not happy, a closeted content human. He’s an uxorious husband, dewy, Lapinsky a constant in conversation. “The long-suffering wife,” as he describes her.

“He’s an anxious person. He’s a worried, worried, worried person. He’s in pain from the worry and anxiety. But he’s not depressed or sad,” Lapinsky says. “We can both go down to the dark side. He and I will do anything for the joke. It’s partly why it works so well.”

On set, Susie Essman says, “everyone loves Lewis. There’s never a harsh word. He’s so generous.” He has friends, fans, sobriety, enough money that he doesn’t have to tour constantly. He stopped therapy seven years ago.

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“Curb” launched in 2000, 10 seasons over two decades, produced on Larry Time, because, when you’re the co-creator of “Seinfeld,” you can do as you please. The show has no script, merely outlines, “the most ideal thing,” Lewis says. It’s helped attract new, younger fans and freed him from touring. He adores this season “because it got back to where it started, with real simple stuff.” Lewis is in most of the 10 episodes.

But: “It’s killed my acting career.”

The role doesn’t exactly show range — unless you include hand motions.

Lewis had a decent run on the sitcom “Anything but Love” with Jamie Lee Curtis (so many vests), starred in the movie “Drunks” and had a cameo in “Leaving Las Vegas.” He played Don Rickles’s son on one season of “Daddy Dearest” and a rabbi on “7th Heaven.”

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But: “I got pigeonholed as the neurotic, Jewish guy.”

Lewis’s greatest role, his Hamlet, has been himself. He’s one of comedy’s great gesticulators, a master of the shrug. Since the 1980s, the only changes to his look are due to time and gravity. Lewis is the original hair comedian, a waterfall of Farrah waves, and baggy black clothes to match the mood. “I bet his underwear is black,” says J.B. Smoove, who plays David’s housemate, Leon Black. (Lewis: It is.)

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The long-glabrous David, Lewis claims, intentionally included a close-up of his nascent bald spot on a recent episode. “He was ecstatic,” says Lewis, who dubbed him “Larry the hog,” as he’s the center of every shot, unwilling to allow Lewis to share a meaty scene with Smoove and Essman.

“There is nothing predictable about Richie,” says Essman, who toured with him. “His brain works differently. He seems like a jazz musician, improvising and riffing. He shows this deep, deep vulnerability. He’s such an open soul. He’s taught me to be fearless.” (Unlike her cesspool-mouth “Curb” persona, Essman swears only once during the conversation: “It’s called acting.”)

Lewis tends to riff in his performances, like his hero, Lenny Bruce, so no two performances are the same, making a comedy special, where the identical routine is filmed on several nights, nigh onto impossible. Lewis is credited with coining the phrase “date from hell,” launching countless iterations of “whatever from hell.” He likes to say about his comedy, “I go on a long tour and make people happy that they’re not me, and then they go home.”

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In his comedy, Lewis is invariably his own punching bag:

“I quit therapy because my analyst was trying to help me behind my back.”

“Life and mental illness aside, the only reason to stay miserable is life or mental illness.”

Lewis stores “about 20,000 pages” of jokes on his computer. Early in his career, he scribbled bits on legal pads, subjects such as “birthdays,” “sex,” “intimacy” and, naturally, “my mother.” In 1989 at Carnegie Hall, he appeared with six feet of yellow sheets taped together, 2½ hours, two standing ovations. The night was “the highlight of my career.”

But afterward, he got plastered in the dressing room “and made a complete jackass of myself.” Lewis had to ask his sister if the ovations actually occurred. “And still it took me five years to get sober.”

Episodes from his life seep into “Curb.” Fighting over the check (Episode 3 this season) is a constant in the Lewis-David friendship. “I always get there early and give the restaurant my credit card,” Lewis says. “We placed our order. Been there just five or six minutes, and Larry realizes he has a poker game at Steve Martin’s and leaves. And I’m eating alone, stuck with a $400 check.”

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David says: “The key ingredient to his humor is his honesty. Richard has a bad relationship with himself — most comedians do — but he can express it.”

Comedians “have a unique filtration system,” Smoove says. “We can take the amazing pain of being ourselves and reprocess it through our bodies and give it to you in a manageable form. It takes a lot for a comedian to give that to you. We have a high tolerance for love. And a high tolerance for pain.”

Lewis’s gift, Smoove says, is “to turn it up as much as possible. His act is as the Prince of Pain, but it’s his management of that pain. He has to have control of his happiness, too.” Smoove contends, “Somewhere in there is a puddle of glee.”

Lewis claims to be most content sitting around his home watching European classics, Truffaut and Fellini. “If I had the courage, I would write a very weak Ingmar Bergman film. I love his darkness,” he says. Or a dramatic play, citing Eugene O’Neill. “What started with darkness, I’ve spun it into comedy. If I wrote the darkness, I’d come full circle.”

“Curb,” he concedes, spoiled him. Life, as David might note, is pretty, pretty good. Lewis is not sure what he’ll do next or if he’ll return to doing standup.

But: It could be the pain talking.

Correction: Due to an editing error, this story initially stated that Larry David was on the left side of a photo, when he was actually on the right side.