Ms. Line was hired, and the characters’ signature looks — stripes, leather jackets, trench coats — have been the subject of much discussion ever since, with blogs devoted to what the characters wear. “Every single day I get tweets, Facebook messages and Instagrams from girls who line up their clothes next to photos of the characters,” said Ms. Line, who also believes that “Pretty Little Liars” is influencing retail. “I have seen feather earrings and black-and-white-stripe dresses in stores.”

But Ms. Line has bigger ambitions than just glimpsing her influence while shopping. “I’m a Leo, I’m 6 feet tall, I love being in front of the camera,” she said. “I’m a vegan and do charity work and mentor kids. I am destined for something.”

“Ultimately, I want to do a fitness line,” she said. “I want a book and a show.”

Years ago, if costume designers were known at all, they worked in movies. Think of studio powerhouses like Adrian, who worked on MGM productions like “The Wizard of Oz” and “The Philadelphia Story,” or Edith Head, of Paramount and later Universal, who designed costumes for Grace Kelly and Audrey Hepburn.

Today, even successful movie costume designers like Catherine Martin, who did the designs for “The Great Gatsby,” and Trish Summerville who is doing the next “Hunger Games” movie and will sell a line, Capitol Couture by Trish Summerville, on Net-a-Porter, don’t exactly cut outsize figures.

But as television has gained more respect as a medium, there has been a coattail effect on some of its costume designers, who say that their work there gives them greater opportunity than current cinema to influence the culture at large.

“The movie genres popular right now have to do with designing vampires and superheroes,” said Rebecca Hofherr, the costume designer for “Elementary” on CBS. “TV deals with more realistic issues and more realistic clothing.”

And some, like Janie Bryant of “Mad Men” on AMC, whose revival of midcentury styles is now a frequent reference on high-fashion runways, are practically becoming brands unto themselves.

Over the last three years Ms. Bryant, who is writing a book and developing a reality-TV competition with the working title “Janie Bryant’s Hollywood,” has struck deals with Maidenform, Hearts on Fire Diamonds (for which she is also a model), Banana Republic and Cosmopolitan Russia. When Ms. Bryant designed a suit for Brooks Brothers based on Don Draper’s look, it sold out of all stores and the Web within 10 days, said Arthur Wayne, the vice president for global public relations for the store, adding, “These types of collaborations help the consumers think of us differently.”

Thanks to a new division at the Matchbook Company, an agency in a town house on a leafy block of Murray Hill that is currently managing the careers of Ms. Bryant and Ms. Line, consumers may also soon be thinking of television costume designers differently.

“We want the public to recognize them as people, not just behind the scenes,” said Linda Kearns, the vice president for brand development at Matchbook, which also represents the costume designers Tom Broecker (House of Cards”), Dan Lawson (“The Good Wife”), Jenn Rogien (“Girls,” “Orange Is the New Black”) and Lyn Paolo (“Shameless,” “Scandal,”), as well as athletes, models and speakers. “We are focusing on the TV designers because there’s a bigger attachment when the characters of the show enter your home and life each week.”

Although she would like to represent the designers for the shows “Downton Abbey” and “Nashville,” Ms. Kearns said she has turned down plenty of potential clients.

She met Ms. Bryant after Ms. Kearns’s business partner, Kristi McCormick, booked her for an appearance at Nordstrom in Seattle, sponsored by Joseph Abboud, offering style tips to men. “I just had this sense she could be so much more,” Ms. Kearns said.

Ms. Bryant pointed out that her field amounts to a comprehensive course in clothing design. “It’s so vast and so varied,” she said while attending New York Fashion Week with Ms. Paolo. “It’s not only limited to women’s wear, it’s men’s wear, children, all socioeconomic backgrounds, all different bodies.”

Television has certainly had its share of memorable fashion moments, from Mary Ann’s red-and-white gingham dress to Bill Cosby’s sweaters. But few of its designers are widely remembered, other than the late Nolan Miller, for “Dynasty,” and Patricia Field, for “Sex and the City.”

“The buzz started towards the end of the first season, and by the beginning of the second, it just exploded,” Ms. Field said of the latter show, on HBO. “It was like sitting at the bottom of an atom bomb.”

Her mix of high and low price points, designer and street wear, was new on screen, and “Sex and the City” was credited with starting crazes for nameplate necklaces, Manolo Blahnik shoes, flower corsages and visible bra straps. Ms. Field designed collections for Payless Shoes and HSN and was approached to do a reality show (she also recently worked on costumes for “The Other Woman,” a movie starring Cameron Diaz). “It was a lot of fun to be acknowledged, actually,” she said. “I was recognized on the street.”

Eric Daman, who did work for “Sex and the City” and went on to the CW show “Gossip Girl,” said that by the latter show’s sixth season, it was “getting one-of-a-kind couture from Paris.”

“They wanted their wares on Blake Lively,” he said.

Now working on “The Carrie Diaries,” the “Sex and the City” prequel on CW, Mr. Daman is represented by William Morris Endeavor Entertainment. He has designed a prom collection for Charlotte Russe, and a Native American-inspired line for Atelier Swarovski. “Creating your own brand is the dream,” he said. “Being a costume designer is a good job, and capitalizing on it, you need a team around you that helps push that forward.”

For her part, Ms. Rogien, of “Girls” on HBO and “Orange Is the New Black” on Netflix, has become a spokeswoman for Aerie, the intimate-apparel line from American Eagle, and one of Gap’s Styld.by experts. “I love the realistic and the gritty and elegant and tailored,” she said from a 53-foot-long wardrobe truck at Kaufman Astoria Studios in Queens, where she was working on the second season of “Orange Is the New Black,” the prison drama.

Mr. Lawson, of “The Good Wife” on CBS, said that, after being stalked in stores by fans of the show, he is developing a line of clothes for professional women. “People ask, ‘Can you just pick out one thing for me?’ ” he said. “Christine Baranski and Julianna Margulies will be walking down the street, and real female lawyers approach them and say: ‘I want to look like you. Where do I get it, how can I get it?’ ”

He has also collaborated with PONO on jewelry. And he said he has consulted on styles for Diane Sawyer. “We came up with some looks and zhuzhed things around with her,” he said.

But confuse costume designers with stylists at your peril. “I work with the script, the director, the writer and the actor to figure out what the costume needs to do to help the actor inhabit that person,” said Audrey Fisher, the costume designer of “True Blood” on HBO. “Stylists are about satisfying the needs of the actor on the red carpet. They’re telling a story, too, but it’s really the story the actor wants to tell.”

Mr. Daman said he gets from 5 to 15 inquiries a day from people interested in becoming costume designers. “It’s not just walking into showrooms, it’s not the Rachel Zoe lifestyle at all,” he said. “I was doing fitting for 12 hours yesterday.”

Mr. Broecker, of “House of Cards” on Netflix, who has a master’s degree in costume design from the Yale School of Drama, was careful to draw a distinction between himself and the masters of the atelier. “You’re at the mercy of fashion designers to interpret your character on some level,” he said. “But we can help designers see their product in a different way to further it down the road. For Robin Wright’s character, there might be one Armani dress that works and seven others that don’t, one Zac Posen dress that works. It starts to all cohesively come together, and you’re like, ‘Oh, here’s the character, and here’s the style of the character.’ A designer may see that and think, ‘How can I extrapolate that into a collection?’ ”

Ms. Paolo, of “Shameless” on Showtime and “Scandal” on ABC, is also cautious about overinflating the role of the costume designer, though she is considering a book of “Scandal”-inspired tips. “People send me images of themselves, saying, ‘I have a job interview and would this work?’ ” she said. “I respond and tell them the truth. I try not to hurt their feelings.”

But “you don’t want to overexpose your show,” she said, and moreover, “My ‘Shameless’ producer told me the kids were starting to look a little too fashionable.”