The subject at hand was the spank bank—as in, “Who’s in your spank bank?”

As in, when self-pleasure is your goal, whom do you fantasize about?

A firefighter friend of Mr. Leary’s—upon whom the actor-comedian partially bases his Rescue Me character, New York firefighter Tommy Gavin—mentioned that a smoke-eater colleague let slip that another fireman’s wife featured prominently in his spank bank. The disclosure, unsurprisingly, led to a heated firehouse argument.

After Mr. Leary heard the story, the premise quickly got written into an early episode of the fourth season of Mr. Leary’s hour-long firehouse drama, Rescue Me, which returns tonight to FX, the cable channel. It became part of a bawdy scene in which Tommy and his crew share the names in their own particular fantasy pantheons.

Tommy: “Ellen DeGeneres.”

Sounds of incredulity.

Tommy: “Hey—you ever seen her dance?”

But when the question was put to Mr. Leary himself (“So—is it too personal to ask who’s in your spank bank?”), sitting in a Soho boîte north of Canal Street, Mr. Leary’s cheeks reddened. Just a little.

“Umm, that’s reserved,” said Mr. Leary, momentarily at a loss for words.

On the day of our meeting, he wore a black linen sport coat over a dark olive T-shirt, jeans and work boots. In person, Mr. Leary is taller than he seems in films like The Ref or The Thomas Crown Affair. Based on his machine-gun spray of comedy—whether as MTV’s Nicotine Fiend (the ads that first got him noticed) or his comedy specials, No Cure for Cancer (1992) and Lock ’N Load (1997)—you would assume there’s a small-man complex at work here, but he’s tall and solid.

As he approaches 50, his face seems constructed of sharp edges, right down to that prominent scalene triangle of a nose. He’s more laid-back than you’d expect—at least until he gets wound up. Such as when he starts talking about how he’s learned to deal with the public.

“I was reading David Mamet’s new book and I threw it in the trash, but then I pulled it out, because why give him the satisfaction after I paid good money for it?” Mr. Leary said, warming up. “I love his writing, but I hate it when it’s in books. But he said something that stuck with me. Essentially, it was that I’m at the age where I don’t give a shit what people think.

“Like, I was talking to someone and a stranger came up and said, ‘I don’t mean to interrupt,’ and I said, ‘But you just did.’ Or there was this photographer following me and my kids, taking pictures of my daughter, who obviously didn’t want her picture taken. And I finally said, ‘Aren’t you ashamed of yourself, bothering a 15-year-old girl who doesn’t want her picture taken?’ And the guy kind of slunk away. Sometimes, when you say the flat-out truth, that’s enough. I usually don’t have a can of beans handy, like Hugh Grant; the only thing I have to throw is my cell phone, which I need. So the truth, well, it’s easier than throwing things.”

LAST SEEN UNCONSCIOUS AND TRAPPED in a burning beach house during Rescue Me’s Season 3 cliffhanger, Tommy Gavin lives on this summer as TV’s most morally complex character. With The Sopranos over and done, it’s time for Rescue Me to claim the mantle of best show, with Tommy Gavin as its compelling—disgusting, lovable, drunk, sexy, insane—central figure.

Tommy is selfish, self-destructive and ethically challenged—a scoundrel who also happens to be a hero, or perhaps vice versa. A lapsed Catholic who still totes around the steaming heap of guilt dumped on him by years of parochial school, Tommy’s rakish approach to life makes him impossibly appealing—and tragic, of course, when he tries and fails to do better.

“He’s actually based on two friends who are firefighters,” Mr. Leary said. “I talk to these two guys all the time, just to catch up on what’s going on with them and their families—and every time I do, there’s three more episodes right there.”

Tommy’s also an egomaniac, and an equal-opportunity asshole, which of course makes him irresistible to women. Here in Season 4, Tommy’s marriage is in the toilet (he’s always treated it like a job that he was free to punch out of when it got too demanding), but it isn’t over, though it probably should be. In the course of Rescue Me’s first three seasons, Tommy had affairs with everyone from his brother’s ex-wife (as revenge for his brother getting involved with his ex) to Sheila (Callie Thorne), the 9/11 widow of his best friend (whose ghost regularly talks to Tommy), to Sheila’s kid’s teacher (who was banging Sheila’s teenage son). And he nearly always got caught.

Tommy struggles with alcoholism (it got him into a fistfight with his cousin, a priest), probably because he also deals with a lot of death, and not just the people he loses in burning buildings: During the first three seasons of the series, his mother (natural causes), his brother (a cop shot on a stakeout) and his young son (hit by a drunk driver) all died.

The mammoth death cloud hanging over all of it, of course, is 9/11; Tommy’s massive case of survivor’s guilt is marbled through his psyche and the story lines. Yet Rescue Me’s writers regularly perform the comic alchemy of transforming even that darkest material into unexpected laughs—the kind of tension release that comes from sticking a pin to a balloon. In the black-humor world of firefighters, Tommy is a champion ball-buster in a game where needling your colleagues is an Olympic-level blood sport.

Yet what gives Rescue Me its tang, its heft, its compulsive watchability, is this: Antihero though he may be, Tommy Gavin is still a guy who makes his living saving the lives of strangers, even if he sees it as penance for all the moral disorder he creates in the rest of his life.

“The redeeming factor for Tommy—for all these guys, really—is what they do and how they do it,” Mr. Leary said, tucking into a tuna-salad sandwich. “There’s a lot of forgiveness in the fact that they run into burning buildings for a living. There’s always a forgiveness factor.”

“Tommy is dangerous enough to be a complete mess,” said Peter Tolan, who co-created the show with Mr. Leary and produces and writes it with him. “That’s the real magic act. Tommy’s a real dumb shit—yet, because of Denis, more people than not are pulling for him and sympathetic to him.”

Mr. Leary, who’s been with his wife for 25 years and has two teenage kids, shares little with Tommy beyond a sense of humor—that needling, sarcastic edge that blossomed “at 12 or 13, the cognitive years, when I figured out that everything they told me at Catholic school was wrong—that everything they said was bad was actually good.”

In fact, according to Mr. Tolan, Mr. Leary is actually something of a sweetheart—an involved parent who looks out for his friends (when he isn’t busting their hump). Mr. Tolan recalled a recent phone call in which he and Mr. Leary chatted about a script Mr. Tolan was writing. When Mr. Tolan asked if there was anything else, Mr. Leary responded, “Well, I love you.”

“I asked him if he was high and he got offended,” Mr. Tolan said with a laugh. “I think that would surprise people.”

Absolutely, considering that Mr. Leary’s breakthrough was a caustic stand-up show (1992’s No Cure for Cancer) that included a song proclaiming, “I’m an asshole.” But get him talking about firefighters and this onetime choirboy gets absolutely gushy.

He created his own charity, the Leary Firefighters Foundation, after a massive 1999 fire in his hometown of Worcester, Mass., killed a cousin and a close friend who were battling it. The heroism of firefighters who died on 9/11 (where he also lost friends) led him to expand his efforts so that the foundation now serves as a national advocate for the public servants and a fund-raising source for firefighting equipment and training facilities. Mr. Leary has his own theories about what compels people to that dangerous calling.

“They don’t do it for the money—and they sure don’t do it for the pension, considering the risks,” Mr. Leary said. “The common ground I’ve found among the firefighters I know is that, first, it’s a job that makes a difference. Second, a certain percentage of them are action junkies. And third, they have an incredibly boundless amount of courage. It takes that to run into a burning building; until it happens, you just don’t know if you possess it.”

Prior to creating Rescue Me, Mr. Leary spent a couple of frustrating seasons writing, producing and starring in The Job for ABC—a show about New York cops with a similarly button-pushing comic sensibility that suffered from network indifference.

“They had so little interest in it at ABC,” Mr. Leary said. “Part of me was actually happy when it was canceled. Peter and I developed a working relationship unlike any other I’d ever had. I felt like I’d been to college on that show.”

“That show was like training wheels for Denis for this one,” said Mr. Tolan, who Mr. Leary initially approached to collaborate with because he liked Mr. Tolan’s work on The Larry Sanders Show. “He has a lot more tools now.”

Working on The Job, Mr. Leary said, taught him what it means when a major network tells you “yes.”

“Network guys, when they say ‘We love the idea,’ what they mean is ‘Let’s see what the focus groups think,’” Mr. Leary explained, one hand raking that lank blond hair—the best hair on TV—from his forehead. “These guys get in that job and their gut goes away. Like Presidential candidates.”

A graduate of Boston’s Emerson College, Mr. Leary used stand-up comedy as a springboard to a movie career. He has appeared in more than three dozen films, outings as diverse as Wag the Dog, The Thomas Crown Affair and Disney’s forgettable adventure-comedy, Operation Dumbo Drop. He regularly trolled the indie side of the street as well: Alan Rudolph’s The Secret Lives of Dentists, Campbell Scott’s Final. But since Rescue Me’s 2004 debut, he’s not anxious to go back to acting on the big screen.

“Most movie scripts suck and they’re all about the money,” Mr. Leary said. “And I don’t need the money. At this point, I’ve got the reputation: You can call him, but he ain’t gonna do it.

“Paul Newman is one of the only actors left I’d like to work with on a movie—and he just retired. But I have a secret evil plan to get him on Rescue Me. When he retired, he said he couldn’t memorize lines; great, we won’t give him many lines. And he doesn’t like to travel; fine, we shoot in New York. I know he could play an irascible uncle of mine. Maybe he’ll read this.”

MR. LEARY IS NO DOUBT THE FACE of Rescue Me (have you seen the posters? neck veins and all?) but the bulk of his energy is devoted to writing the show. He writes, co-writes or rewrites every episode of the show and has for its entire run.

And once Rescue Me finishes shooting the current season’s episodes, Mr. Leary will shift gears to produce Canterbury’s Law, a legal drama starring Julianna Margulies (with a pilot directed by Mike Figgis, set for January on Fox). He and Mr. Tolan also created a cop-show pilot for NBC, Ft. Pit, that didn’t make the fall lineup: “It’s a business, like selling biscotti,” Mr. Leary shrugged.

He’s written a movie he hopes to direct and is also writing a book (“It’s not fair to call it a book; it’s really a printed version of my subconscious”). And he still does stand-up, sparingly, reserving his New York appearances for the annual New York Comedy Festival in the fall. He still reads five newspapers a day, riffing on what he sees: “That’s the great thing about stand-up,” he said. “You’ve got a show at 8. You walk out, there’s a mike—and that’s it.”

There’s no shortage of potential material out there, whether it’s the Presidential candidacy of Rudy Giuliani (“the worst friend firefighters ever had”) or why so much popular entertainment is so terrible: “I believe there’s a reason when you see a really dumb movie or a dumb TV show that are hits. The audience is not being fooled. It’s what they want to see.”

Rescue Me, however, manages to be both smart and popular because FX allows Messrs. Leary and Tolan lots of latitude. There are few taboos with language, sexuality or subject matter: from the fireman who is dating a recently decommissioned nun to, well, that spank-bank discussion. There are still strictures (no frontal nudity, no using the word “fuck”), but Rescue Me doesn’t need them to provoke.

Last season, for example, an Internet controversy erupted over a scene of rough sex between Tommy and his ex-wife Janet (Andrea Roth) that some viewers construed as rape: “That caught us unaware,” Mr. Tolan said. “We thought it was just another trip down Dysfunction Lane with the Gavins.” (To be fair, Janet did utter a few no’s and stop’s before ecstatically consenting.) Meanwhile, in Season 4, Janet has a new baby whose father could be Tommy—or his late brother, with whom she was living after she and Tommy separated.

Still, there was one line FX executives wouldn’t let Mr. Leary cross for the coming season. Fans will be thankful he didn’t.

“I tend to be edgier than most, so I pitched what I thought was a brilliant idea,” Mr. Leary said, with a subversive smile that’s pure Tommy. “I said that, at about the sixth show of the season, the audience should tune in with no previous information about the episode. The guys go to a fire—and everybody gets killed. Which is highly possible. People tune in the next week and there’s no show. Everybody’s dead; the series is over. Now that’s something people would talk about.

“Or how about this, then? Tommy dies. He disappears in a fire and, at the end of the show, they find him dead. And the next week is the funeral. And then the show’s over. Nobody’s ever done that, right?

“They said no. I said, ‘I’ll write you another series.’ But they said no. I guess I don’t blame them.”

After a self-enforced layoff from stand-up of about two months, Mr. Lewis will perform at Comix, a new club in Manhattan’s meatpacking district, on Feb. 23 and 24. He’s eager to get up—and also dreading it, of course. “New York is my home turf – I have so many friends in Manhattan,” he said the other day. “And, tragically, so many relatives. There’s a percentage of my family that I love. But there’s a larger percentage that, when I know they’re going to be there, I feel obligated to really tell how I feel, to go places with my stand-up that I don’t even go with therapy. It makes me want to reach back for the high, hard one rather than holding back. So the pressure for these shows is enormous.”

With his trademark black clothing and peripatetic stage presence—pacing, clutching at his hair, doing a kvetch ballet during each performance—Mr. Lewis is part of a modern tradition of comedy neurosis whose antecedents include Woody Allen and Shelley Berman, now Mr. Lewis’ co-star on Larry David’s Curb Your Enthusiasm. “We’re both worrywarts—we both live on the dark side of life,” said Mr. Berman, 82. “But he’s very nervy. He cuts himself wide open when he works. You can see the guy bleed.”

Mr. Lewis may still bare his soul in his act, but he does so without the security blanket that he dragged onstage with him for years: taped-together sheets from a legal pad, on which he would write lists of comic premises that occurred to him at all hours, to remind himself of what he wanted to talk about. Eventually, the list would grow so large that when Mr. Lewis spread it out on the piano that inevitably graces his stage, it looked like some oddball quilt assembled for a Staples commercial.

He still generates material with prolific abandon, typing it into his ever-present laptop, where he stores about 20 hours of new material, which he scrolls through endlessly before and between shows. “I’m such a madman—I’m so obsessed about the show, but that’s who I am,” Mr. Lewis said. “I’m just so wired by my time onstage, my head is filled with images. It’s terrifying, but it’s also exhilarating. I’ll never not work like this.”

He’d like to take another shot at Carnegie Hall, where he played a sold-out 1989 show with six taped-together sheets of paper. “If I did everything on the list, we’d still be there,” Mr. Lewis said. He’d also like to be sober this time. While he wasn’t drunk onstage (“I was one of those functional kind of guys”), he barely remembers the two-and-a-half-hour show or the multiple standing ovations at the end. And his girlfriend at the time erased his only tape of the show.

“My sobriety has opened so many synapses that were hidden from years of drinking and drugging,” said Mr. Lewis, who discussed his alcohol problem, and his tortured family life, in his 2000 memoir The Other Great Depression.

“He was always good, with his malfunctioning family and his view on life from the dark side,” said his friend and fellow comedian David Brenner. “It wasn’t the underbelly of poverty; it was the dark side of mental illness.” Mr. Brenner recalled a discussion in which Mr. Lewis told him that he’d been in therapy, three times a week, for 17 years: “I told him, ‘If you had a toothache, and you went to the dentist for 17 years and you still had that toothache, you’d have to figure there was either something wrong with that dentist—or with dentistry in general,’” Mr. Brenner said. “He looked at me like the RCA Victor dog—he didn’t understand what I was talking about.”

“I was born to talk about myself,” Mr. Lewis said. “Had my parents listened to me with any degree of interest, it wouldn’t have happened. The whole house should have had funhouse mirrors. I didn’t trust the people who knew me; I needed to go onstage in New York City and talk to strangers to validate me. That’s why I got married late: I had these trust issues, and I figured there was a chance they’d linger.”

A self-professed “affection addict” who admits to cheating on virtually every ex-girlfriend (a list that includes Nina Van Pallandt and Debra Winger), Mr. Lewis used to date extremely young women—either ones who were downright nasty (“because I was getting what I deserved”) or girls who were so dewy and unformed that he had to play Pygmalion. “It was like, ‘This week we’ll watch all of Fellini, then it’s on to Cassavetes and Truffaut’—everyone had to catch up to Richard.”

Then he met Joyce Lapinsky, a woman in her 40’s who worked in music publishing, at a playback party for a Ringo Starr album. “It triggered what she calls ‘the snake dance,’” Mr. Lewis recalls. “I might as well have been a 9-year-old. I was putting on a show for this woman.”

After seven years of dating, Mr. Lewis took Ms. Lapinsky to meet his therapist. “It’s sad—had no confidence in my ability to select a mate,” he said. The shrink listened to his patient complain about some minor communication problem that he saw as an impediment to further commitment with Ms. Lapinsky, then erupted. “In a voice that was almost satanic—it was so dark and loud that it seemed to echo through the neighborhood—my therapist screamed at me, ‘This is as good as it gets!’” Mr. Lewis said. “It shook me to my core.”

Still, there was one hurdle: Mr. Lewis’ house, perched above the Sunset Strip in Hollywood, which he refers to as “the museum.” All of the vertical surfaces of the hillside structure’s multiple floors—and most of the horizontal ones—are covered with Mr. Lewis’ immaculately displayed collection of memorabilia and souvenirs from three-plus decades in show business: framed photographs, autographs, paintings, posters and other minutiae of Mr. Lewis’ artistic heroes, mentors and inspirations: everyone from Jack Kerouac to Groucho Marx to Lenny Bruce, Buster Keaton to Jimi Hendrix to John Cassavetes, Oscar Levant to Johnny Carson to Mickey Mantle.

“I knew that, if I wound up being with you, I would have to have my own home,” the minimalist Ms. Lapinsky, now a program-development consultant for Urban Farming, a nonprofit organization, told him. She got a cabin in the mountains 80 miles away, and she and the outdoors-averse Mr. Lewis (“I’m literally allergic to the sun,” he said) divide their time between the two domiciles.

“Joyce has such a stabilizing effect on him,” said Susie Essman, another Curb co-star, who has known Mr. Lewis for two decades. “Everybody is looking for that one person in life who will love you unconditionally, and he’s found that with her.” She paused, laughed and added: “And yet he’s still miserable.”

Mr. Lewis recently received the newly released DVD set of the first season of Anything But Love, the sitcom on which he starred with Jamie Lee Curtis for the better part of four seasons, starting in 1989. Aside from the way his elaborately coiffed hair looks on the show (“Like two beavers standing up and having a fistfight,” he said), it reminds him of how long he’d been working before he got that break—and how long it’s been since that show ended. Since then, he’s starred in a couple of short-lived sitcoms (including Daddy Dearest with Don Rickles and Hiller and Diller with Kevin Nealon), and done guest shots on everything from Alias to The Simpsons. But acting roles come only sporadically.

“It’s been baffling to me,” Mr. Lewis said. “I had a wonderful flight with Gary Sinise recently, and he said what I hear from a lot of people: ‘How come you don’t do my show?’ I didn’t say it, but I thought: ‘Ask your casting director!’

“Playing Richard Lewis on Curb is the greatest acting role of my career—but, ironically, it makes it even more difficult for me to be considered for other parts,” he continued. But Mr. Lewis wasn’t really complaining. “I’m very grateful for my stand-up career,” he said. “I mean, I was broke for the first 11 or 12 years of my career; I lived in hovels. I guess that’s why I relate to Kafka.”

“You have to understand that, in the range of happiness, his gauge doesn’t go up to 100,” said Mr. Brenner, who lent Mr. Lewis money in those lean years. “But right now, he’s at a 40 or a 45—which is at least 20 points higher than it used to be. Right now, he’s much happier than I’ve ever seen him.”