Her onscreen presence takes on many variations, but she is easily recognizable by a few defining traits. Other than her size, she is almost always black. She typically finds herself in an exchange that is either confrontational or embarrassing. And her best line is often little more than a sassy “Mmmm hmmm.”

This caricature, playing on stereotypes of heavy black women as boisterous and sometimes aggressive, has been showing up for some time in stand-up comedy routines and in movies like “Big Momma’s House’’ and “Diary of a Mad Black Woman.’’ Often, the pieces are produced by directors and writers who are black themselves.

With black creators giving more acceptability to the image, it is now starting to appear more often in television commercials as well. Most recently some variation of this character has appeared in commercials for Dairy Queen, Universal Studios and Captain Morgan rum.

But despite the popularity of such characters among blacks, the use of the image of big black women as the target of so many jokes is troublesome to some marketers and media scholars.

“It is perpetuating a stereotype that black females are strong, aggressive, controlling people,’’ said Tommy E. Whittler, a marketing professor at DePaul University. “I don’t think you want to do that.’’

To be sure, sassy overweight black women appear to represent only a small fraction of the African-American actresses who appear in commercials. Marketers have made strides in recent years toward making advertisements with a more diverse cast of characters.

Blacks regularly appear in commercials selling products as diverse as toothpaste, credit cards and erectile dysfunction medication. Indeed, according to several academic studies, over the last 15 years the number of blacks appearing in commercials has been roughly proportional to their share of the American population, about 14 percent.

“Over the years it’s evolved,’’ said Fay Ferguson, co-chief executive of Burrell Communications, an advertising agency that specializes in marketing toward black consumers. “We’ve come a long way in how we see black women in advertising.’’

Stereotypical portrayals of blacks in commercials have drawn criticism from civil rights groups for decades. Some of the earliest and most iconic examples of blacks in advertising — Rastus the Cream of Wheat chef, Aunt Jemima, Uncle Ben — showed blacks in subservient roles that recalled the days of slavery.

Those images have been toned down over the years (Aunt Jemima’s red bandanna, for example, was replaced with pearl earrings and a lace collar in 1989) and are no longer as overtly stereotypical as they once were. And now there are many examples of blacks presented in middle-class settings and engaged in mainstream activities.

To some, the freer use of overweight black women in comic situations suggests a welcome change that reflects a broader acceptability of blacks in the media. But others find the recurring use of the image a return to a disturbing past.

And some say these images may serve to exacerbate misunderstanding between whites and blacks.

“Not only are we being given images of who we are supposed to be, but others are also formulating their images of us based on that,” said Marilyn Kern Foxworth, an author and marketing expert who studies how blacks are portrayed in advertising. “People have already determined who we are and how we’re going to react in certain situations.”

The heavy black female makes one of her latest appearances in a commercial for the Dairy Queen Blizzard. In the spot, a man boarding an airplane sets his ice cream shake down so he can load his bag into an overhead compartment. As he reaches up, another passenger on the plane starts eating the Blizzard. Seeing this, the first man lets go of his bag so he can reclaim his Blizzard and inadvertently drops his luggage on another passenger’s head.

That unlucky passenger happens to be an overweight black woman who lets out an irritated gasp that reminds all the passengers around her who not to mess with.

Rick Cusato, executive vice president for Grey Worldwide, the firm that wrote the campaign for Dairy Queen, said the script was not written with a black actress in mind.

“We basically cast the funniest person,” he said. “We didn’t specifically cast for a black woman. We said, ‘Wow, she’s really funny.’ And she happened to be black.”

Another new Dairy Queen commercial features a similar character — played by the same actress — working as an airport security screener. When a man tries to walk through a metal detector eating a Dairy Queen burger, her eyes dart disapprovingly downward at him. Then she barks, “Uh, uh. Get on!” directing him to walk through again.

Michael Keller, Dairy Queen’s chief brand officer, said the company considered actors of all sizes and races before making a decision. “We looked at male body builders, really big tall women. We looked at just about everybody we could,” he said. “She projected an image that was everything we wanted it to be. This is just a strong woman being herself.” He added that the company had not received any complaints about the ads being racially insensitive. But to some these images are troubling.

“It’s not an accident that she’s African-American and heavy,” said Howard Buford, founder and chief executive of Prime Access, an advertising agency that creates commercials marketed toward minority audiences. “There’s certainly a long heritage of large African-American women who are kind of sassy and feisty and humorously angry. There’s a sense that this whole value system is O.K. again.”

Large black actresses have had recurring roles in commercials over the years, and often are cast in roles where their aggressiveness is a defining trait. The heavy black spokeswoman for Pine Sol was one of the first to embrace the role. Her aggression was aimed at household dirt, however, not people. In a recent commercial for Captain Morgan rum, a large black woman berates her man for playing dominoes and making her late.

In one recent Twix commercial, a full-figured black woman asks her boyfriend if her pants make her rear end look big. As the camera focuses on her plump backside (exaggerated by the camera for effect), the man stuffs his face with a Twix bar and mumbles an indecipherable answer.

Pleased with his response, the woman walks away. She is not shown being aggressive or loud, but the commercial leaves the impression that if the man had given the wrong answer, she might have erupted.

A series of Universal Studios commercials star a heavy black woman who is accompanying her children on a Jurassic Park ride. Frightened by the ride, she roars and buries the heads of her two young children in her bosom.

Black advertising executives have noticed the stereotype.

“There’s an image out there of black women being boisterous, overbearing, controlling and extremely aggressive in their behavior,” said Carol H. Williams, who runs her own advertising firm in Oakland, Calif., that specializes in marketing toward blacks. “I really don’t know why that stereotype is laughed at.”

Some have trouble with the new commercial images in part because they are being created by white writers.

“There are images of African-Americans created for white people by white people and there are images of African-Americans created for African-Americans,’’ Mr. Buford said. “And there’s a big difference.”

The lack of diversity on Madison Avenue has been a long-standing issue. In fact, the New York City Commission on Human Rights is investigating the hiring practices of advertising agencies in the city and is looking at how they have approached employing blacks.

Jannette L. Dates, dean of the communications school at Howard University, said that while whites and blacks could watch the same portrayal of a large black woman on television and laugh, they are laughing for different reasons.

Some whites, Ms. Dates said, may laugh thinking, “Wow, she’s so ridiculous. My people aren’t like that.” She added: “They wouldn’t consciously feel that way. But there is something going on subconsciously because that’s what advertising is all about. They’re trying to tap into some feeling, some emotion, some psychological hang-up.”

Blacks, meanwhile, might laugh because they can identify with the character, Ms. Dates said. “It’s for both the people who want to snicker and say, ‘See, that’s how they are.’ And for people to say, ‘There’s one of us.’ ”

Orlando Patterson, a sociology professor at Harvard, amplified that point. “To the black audience, this may be, ‘You do your thing, sister,’ ” Professor Patterson said. “The white audience is laughing with her. Then they go back to reality, and they laugh at her.”

But Liz Gumbinner, a creative director at David and Goliath, the agency that developed the Universal campaign, said the broad appeal of the commercials was proof they were not insensitively playing on racial stereotypes.

Noting that a black woman in a recent David and Goliath focus group spoke up about how much she liked the Universal ads, Ms. Gumbinner said: “I wonder if sometimes when you have somebody that is less conventional, they become the most memorable. We use a lot of bald men, and it’s not like we have it out for bald men.”

Ms. Gumbinner and Mr. Cusato of Grey Advertising, however, said no black writers were involved in either of their campaigns.

As is typically the case with racial stereotypes, who is laughing and why is complex and potentially inflammatory. Black actors and comedians have profited handsomely from creating bumptious female characters on TV and in movies, raising the issue of whether they, too, are perpetuating the stereotypes that many find offensive.

Tyler Perry, the filmmaker and actor, created a series of plays and movies, including the huge hit “Diary of a Mad Black Woman,” in which the main character Mable (Madea) Simmons is a no-nonsense overweight matriarch. Mo’Nique, a full-figured comedian, has built a routine on being outlandish, brash and, at times, downright crude.

Mr. Buford, of Prime Access, said part of what makes the comedy of Mr. Perry and Mo’Nique acceptable is that it is written from a personal experience common to many blacks.

“Authenticity makes a lot of difference,” he said. “It’s authenticity born of having lived that life versus having been cast in that role.”