It’s getting a bit tougher for Holt McCallany to walk down the street these days.

While the New York City-born actor has three decades of steady work in television and film under his belt, including memorable roles in Fight Club, Three Kings, and on the FX boxing series Lights Out, he’s getting the most recognition of his career—from critics and fans—for his work in Netflix’s new drama series Mindhunter.

“The response to the show has been tremendous,” McCallany tells Men’s Fitness. “The reviews have been strong and the response from fans has been fantastic. I’m getting thousands of Twitter messages per day from people all over the world. Before? Sure, there were people who came up to me on the street because of Fight Club, or they’re diehard fans of Lights Out—a show I loved, too. But now, it’s all people coming up to me about Mindhunter. I’ve never had that before.”

Mindhunter follows FBI agents Holden Ford (Jonathan Groff) and Bill Tench (McCallany) during the nascent days of the FBI’s Behavioral Science Unit in the late 1970s. The two agents travel the country teaching local cops federal investigative techniques, while developing the fields of criminal psychology and criminal profiling. How they get that done: Interviewing some of the most notorious real-life serial killers in U.S. history, including Ed Kemper (Cameron Britton) and Richard Speck (Jack Erdie).

The perfect way to sum up the series might be this line from McCallany's Tench to the higher-ups at the FBI when he defends Holden's new way of thinking: “How do we get ahead of crazy if we don't know how crazy thinks?" Tench asks.

Holt McCallany and Jonathan Groff on Netflix's series 'Mindhunter'

Digging deep into his Mindhunter role

After a career playing mostly supporting roles, McCallany is getting to show the full range of his talent as Tench, the “chain-smoking, middle-aged bureaucrat” who gets paired up with Groff's wide-eyed Holden. McCallany's balance of the grim subject matter with the witty one-liners that Tench throws at Ford is pitch-perfect, and adds a line of dry humor to every conversation they have. And in Mindhunter, they certainly get to have some interesting conversations.

Many of the episodes feature scenes between just McCallany and Groff going back and forth as they debate criminal theory and analyze the serial killers they’re researching. The long pages of dialogue presented McCallany a challenge that he was up for.

“Jonathan and I both come to the set ready to work, and having done the homework,” McCallany says. “He’s a very talented young man with whom I've had a really good time working. Whenever you're working closely with someone on those dialogue-heavy scenes, you're always running lines together. You’re always figuring out ways to try things with each scene. It's all about collaboration, and about an exchange of ideas.”

Holt McCallany and Jonathan Groff on Netflix's series 'Mindhunter'

While Ford and Tench are presented as opposites in many ways, the characters develop a brotherly relationship through the first season, finding they have much more in common than they initially realized. McCallany says he's relishing the opportunity to play a character for 10 episodes, rather than just a few scenes in a two-hour movie.

“You know they say sometimes when success comes a little later in life, it's sweeter, because you can feel like you really earned it,” McCallany says. “This was an exciting opportunity for me, a big promotion, to be one of the leads on a new show. As an actor, you can work for many, many years, but you're always waiting for the one special role, the role where you have the opportunity to show more sides of yourself than you have in the past. That's certainly happened for me on this occasion, where I can really explore this guy over a long period of time.”

McCallany's shredded-to-fat transformation

McCallany completely dedicated himself to the role, shooting for 10 months in frigid-cold Pittsburgh and going through a bit of a body transformation, gaining 25lbs to play a guy who, in McCallany’s words, “drinks too much, eats crappy food, is on the road 40 weeks a year, and whose only exercise is an occasional round of golf.”

In an era where it’s normal for actors like Chris Hemsworth and Tom Hardy to spend months in the gym getting shredded for a role, McCallany took the opposite approach. Basically, he got fat.

I’m just smoking all the time while we’re shooting. We went through so many packs on the show, there were times when I was lightheaded.

“The camera sees everything, so you make a decision,” McCallany says. “One of the things you have to ask yourself, whenever you're creating a new character, is: What kind of a physicality do I want to bring to this guy? I know that I'm gonna pay a price for it physically, but I want to play this guy a certain way. Tench isn’t a guy who's gonna have like a 'beach boy' kind of body. So I put on the weight, I smoked like he smoked—and boy, I am not a smoker. I like to lift weights, I'm a runner, I box, I did a few boxing projects earlier in my career. I'm determined to get myself back in top shape the minute the director says cut.”

For a guy like McCallany, who spends his free time on boxing, mixed martial arts, kickboxing, jiu-jitsu, high-intensity workouts, and Bikram yoga (his secret weapon for healing injuries faster), transforming into Tench provided a bit of challenge, but McCallany was up for it. The toughest part? All the smoking.

“Bill’s a guy in his 50s who chain smokes,” McCallany says. “I guess on the show they have me at 44, which is very generous of them. I should send the writers a gift [laughs]. But David does a lot of takes, and like I said, you can pay a price when you decide to play a character a certain way. [Bill] is a big smoker, and it’s the '70s, so I’m just smoking all the time while we’re shooting. We went through so many packs on the show, there were times when I was lightheaded. People say, ‘Can't you smoke the herbal cigarettes?’ Well, no—they don't look the same on film, and they don't burn the same way. We wanted to be as realistic as possible.”

Holt McCallany working out

Getting into the 'mind' of Mindhunter

McCallany's preparation wasn’t just physical. The actor spent hours poring over information on the serial killers featured on the show, and read Mindhunter: Inside the FBI's Elite Serial Crime Unit by former special agent John E. Douglas, upon which the show is primarily based.

“We're talking about the real guys and the real crimes that they committed—and these are ghastly crimes,” McCallany said. “You have to do the research. You have to really familiarize yourself with each of these criminals, and the crimes that they committed. Whenever I have some moments when I'm not shooting, I feel guilty if I'm not doing more research. I wanted to understand what an FBI profiler does. Another part of that is remembering I’m gonna prepare for all of this as a guy who is in 1978, which is when we first meet Bill Tench. He has a different worldview.”

Despite the show's grim and sometimes disturbing material, it has its humorous moments, too. McCallany chalks that up to the involvement of Academy Award-nominated director David Fincher, who is an executive producer on the series and directed four episodes, including the premiere and the finale.

“David has an amazing sense of humor, and a very dark sense of humor,” McCallany says. “I think because he's so good at these dramatic stories, people sometimes forget that he can be very, very funny, and that shows in the relationship between Jonathan’s character [Holden] and I. It was very important that we find some levity in our relationship, based upon the fact that we're so different. We're almost like a study in contrasts, because the scenes with the serial killers are very dark and grim and intense. So we thought there could be a juxtaposition to that, where there's some humor between the two agents and our different personalities.”

Holt McCallany of Netflix's series 'Mindhunter'

McCallany is no stranger to working with Fincher, having appeared in both Alien 3 (1992) and Fight Club (1998). McCallany left an impression on audiences and showcased what he could do when given the chance in his Fight Club role: As a member of the cult-like “Project Mayhem,” McCallany kicks a memorable scene when his character inspires the group to recite a now oft-quoted line from the film: "His name is Robert Paulson." That talent for making the most of every scene he’s in shines through again in Mindhunter, with McCallany showing great range in Tench's scenes in the office, and at home with his family, where he's dealing with a strained relationship with his wife and son.

Throwing a punch—and boxing with a legend

McCallany had a similar opportunity to develop a character back in 2011 when he starred in the boxing drama Lights Out, playing a former heavyweight champion struggling with life after boxing and considering a comeback to help support his family. “It allowed me the luxury of revealing things about the character more slowly," McCallany says. “It’s an exciting opportunity to do it again.”

Although the show lasted just one season on FX, the role combined two things McCallany loved: boxing and acting. Earlier in his career, McCallany starred in the HBO film Tyson as legendary trainer Teddy Atlas, and he prepared for the role by training with Atlas and other real-life boxers. By the time Lights Out came along, McCallany had already long been a fan of the sport—partially because his younger brother was a Golden Glove champion boxer—making him a perfect fit for the FX series. McCallany trained with Atlas again to prepare for the Lights Out role, and later worked with Mark Breland, a former Olympic gold medalist and two-time world champion who now trains heavyweight champion Deontay Wilder. When he trained in mixed martial arts, McCallany got the chance to work with former UFC Heavyweight Champion Bas Rutten.

“It was amazing being able to train with these guys that are on the top level of the sport," McCallany says. “Bas is a legend. Atlas is a legend. Breland is a legend. I was fortunate enough to be there because of my work as an actor, but they were willing to accept me, because they knew that I was there to learn and because I was genuinely interested and loved the sport. I love boxing. I even took an amateur fight for USA Boxing in what they call the Master's Division, for guys that are over 35, and I won a three-round decision. I've been really, really lucky to be able to work with some of these guys.”

McCallany applied the same dedication and mindset to his role on Mindhunter, and it's resulted in some of the strongest work of his career. So in this age of Peak TV, McCallany says it's no accident that the spotlight finally found him on TV, rather than on the big screen.

“The wonderful thing about television is that when it's really good, you get to explore a character in much greater detail than you can in any other medium,” McCallany says. “Never before in human art history has a medium existed in which the story can evolve and grow as it can in TV now. In a two-hour movie, or a three-hour play, it has a beginning, a middle, and an end. But here, we have so much more real estate that we can really get to know this character. Some of the best writing that we have now is in television. The studios are making a lot of big tentpole movies, comic book films—I’m a fan of those movies, too. But I feel like the work that I'm doing now is far more interesting, and much more enriching for me, personally.”

Holt McCallany and Anna Torv on Netflix's series 'Mindhunter'

More Mindhunter? McCallany's ready

While McCallany is excited about the reception for the first season, he wouldn’t comment on the future of the series—at least not yet. Netflix has yet to officially renew Mindhunter, but all signs point to it happening. In the meantime, McCallany’s hoping that people keep watching. Well, McCallany had good reason to be excited about the future of the series: Netflix has officially picked up Mindhunter for Season 2.

“My hope is that Mindhunter is going to be one of those iconic shows,” McCallany says. “Something like The Sopranos, The Wire, or Breaking Bad, or Mad Men. One of those shows that people remember and continue to talk about. We're all very proud of it, and the reception has exceeded all of our expectations.”

The first season of Mindhunter is currently streaming on Netflix.