Adam Baldwin

NOW that Adam Baldwin has figured out how to make it look easy — this surly, deadpan, tough-guy thing he does every Monday night on NBC as the monosyllabic secret-agent sidekick on the action-comedy series “Chuck” — he doesn’t mind admitting how hard it used to be.

He was 18 when he got his first taste of movie-star limelight as the title character in the 1980 film, “My Bodyguard,” then roles in summer comedies like “D.C. Cab” in 1983 and smaller parts in prestige films like “Ordinary People” despite not having a clue about what he was doing.

“I was horrible,” he said of some of his early performances, particularly the one in “D.C. Cab” (in which his co-stars included Bill Maher, Gary Busey and Mr. T). “I didn’t know how to work. I didn’t know how to process a character, and, certainly, I wasn’t as funny as I should have been.

“But I did learn a lot of technical stuff, how to be on a set, where to stand, how to do a fight scene, things like that,” he said during a recent interview in a high-end Santa Monica coffee shop, one of those mad-scientist places where they grind the coffee in front of you and serve it in vacuum-sealed flasks on a silver tray. “But then I had to learn how to act. And that just takes some people longer than others. I’m no Leonardo DiCaprio.”

He can say this now that he’s 46, aware of his limitations, proud of the niche he has found. In “Chuck” he plays no-nonsense secret agent John Casey, protecting loose-limbed amateur Chuck Bartkowski (played by Zachary Levi), a computer nerd who has accidentally had the contents of a super-secret government computer downloaded into his brain. But even before “Chuck,” Mr. Baldwin had received sterling reviews and a growing cult following for playing similarly grumpy characters on “The X-Files” and “Firefly.”

“The guy does more with a grunt than most actors could do with a monologue,” said Josh Schwartz, the executive producer of “Chuck.” The extent of Mr. Baldwin’s built-in fan base became apparent to Mr. Schwartz only when the “Chuck” cast appeared at last summer’s Comic-Con International, and “4,000 people went insane whenever Adam said anything.”

Mr. Schwartz said it was the creator and co-executive producer Chris Fedak’s idea to cast Mr. Baldwin as Casey, an idea he embraced as soon as Mr. Baldwin read for the part. “You totally believe him as this N.S.A. agent who’s happy to torture and kill people, but he’s also really, really funny,” Mr. Schwartz said. “He gets the comedy without ever breaking character. And his preparation is astounding. Adam really relishes all these details: How does Casey sharpen his knife and fork before he eats? He’s worked all that stuff out.”

Mr. Baldwin said, “I came up with the idea that Casey has a bonsai tree, and I brought in the Reagan photo that’s in his room.” He added, “I try to make sure the military vernacular is as accurate as possible. For the comedy to work, you’ve got to buy that Casey is a serious guy who’s somewhat incredulous about this geek being inserted into his life.”

After last year’s debut season ended abruptly because of the writers’ strike, “Chuck” struggled to find an audience until just before its holiday hiatus in mid-December, when critics, particularly online, started noticing that the show’s ratings had improved 12 percent from the season premiere. NBC is bringing the show back with a hefty marketing push, including a 3-D commercial during Sunday night’s Super Bowl telecast and a 3-D episode on Monday night.

“I think the network is clearly showing they believe in us,” Mr. Baldwin said. “And I think we’ve found the base line of an audience that’s not going to go anywhere.”

Mr. Baldwin, 6 foot 4 and broad shouldered, was already an imposing presence as a 17-year-old high school student in the northern Chicago suburb of Winnetka — big and quietly menacing, exactly what the director Tony Bill sought for the part of a sullen bully who becomes the protector of a smaller kid in “My Bodyguard.”

“Tony would say to me, ‘Just keep your face in repose,’ ” Mr. Baldwin said. “And I would go: ‘Repose? What’s repose?’ And he said: ‘It just means be relaxed. Don’t move.’ It was great advice, and it’s what I’ve been trying to grasp ever since. Stillness as a technique is still really captivating to me.”

After “My Bodyguard” became a hit, Mr. Baldwin moved to New York, fielded offers from agents and managers who were promising to make him the next big thing. He said he took some parts he probably shouldn’t have taken. He went to London in 1985 for a significant role in Stanley Kubrick’s “Full Metal Jacket.” But the production went on for months, and the film didn’t come out until 1987. By then Mr. Baldwin’s moment seemed to have passed.

“I was given opportunities, I think, that were a little too big when I was a little too young,” he said. “I didn’t measure up. The sports analogy would be if you pulled a guy off the farm team and put him in the big leagues a little too soon. That’s a good way to ruin your arm. Fortunately my injuries weren’t career threatening. They were just emotionally draining.”

He worked steadily through the 1980s and ’90s, bad-guy parts in B movies (including the long-forgotten “Digital Man” and “Cold Sweat”), lots of voice-over work, doing what he had to do to pay the bills. He got married, had kids, played golf, built himself a decent working actor’s career. But it wasn’t glamorous, and it wasn’t always fun.

“I think work begets work,” he said. “I did some things that were certainly labors of love and hard-won parts, but there were others that were just straight-up exploitation movies and terrible to watch and don’t hold up at all. But they do pay the bills.”

All along, Mr. Baldwin said, he felt that his career would pick up when he got older, when he could inhabit more nuanced character roles, to be something more than just big and scary. He was 39 when he got the “X-Files” role, Knowle Rohrer. And he was 40 when he became Jayne Cobb on “Firefly,” a role for which TV Guide named him its Sexiest Newcomer of 2002.

“That was hilarious,” he said. “It just seemed like a mistake, an obvious mistake.”

Now because of his “Chuck” fame, people no longer assume that he’s one of those other Baldwins (he’s not) or that he’s as grumpy as his characters. He envisions a future filled with playing strong, silent types, guys with enough experience to know how the world works, when to take it seriously and when to go with the joke.

“I always did think that when I turned 40, I’d start coming into my own,” he said. “Part of that is just growing and living, suffering and failing and going through the trials of life, having a wife and kids. It humbles you, and going through that humbling process lets you release that self-centeredness, and it’s a very liberating feeling. It lets you stop worrying. I’m enjoying that.”