Advertisers have always sought to influence and persuade - no more so than at this time of year. But since the advent of mass communications, there has been only a handful of ads that monumentally changed the way people think about a product.

DeBeers

Image caption Before the A Diamond is Forever ads, diamond rings weren't the premier symbol of engagement

Through its bold advertising, diamond giant DeBeers did something extraordinary - it managed to convince generations of men and women that the only acceptable symbol of an engagement was a diamond ring.

Prior to the "A Diamond is Forever" campaign - which launched in 1948 and was named by Advertising Age as the most effective campaign of the 20th Century - diamond rings weren't synonymous with marriage or engagement. Peruse 19th Century literature and there's nary a mention of diamond engagement rings.

But DeBeers changed that.

Diamonds aren't particularly rare, but they are the hardest substance on earth - a quality that lends itself to notions of eternity. In pointing that out, and infusing it with notions of romance, DeBeers literally changed Western culture.

Volkswagen

As fans of TV's Mad Men surely know, American advertisers in the late 1950s and early 1960s fed consumers a steady diet of traditional gender stereotypes, earnest claims of product efficacy and aspirational characterisations of the American dream.

Image caption VW's Think Small ad pioneered the use of irony and wit in advertising

Volkswagen humbly shattered those conventions.

The Beetle was a car that Americans did not want. It was made by Germans, whose relations with America were mired in post-war tension. It had an odd shape and a loud, roaring engine.

By contrast, the ideal American cars at the time were enormous, powerful machines, sleekly lined and finished with flashy fins. While American automakers were busy seeking inspiration from the burgeoning airline industry, the VW Beetle seemed stodgy and grounded.

Then, in 1959, VW unveiled its "Think Small" campaign, deliberately highlighting the vehicle's perceived flaw.

There was no pretty girl casting her flirty eye over the car. There was no cool guy driving it. It was nothing short of groundbreaking.

"It was self-deprecating. It was the first post-modern ad," Bob Garfield, an advertising industry consultant and former columnist for Advertising Age, told the BBC.

"Hitherto all advertising had been as serious as a thrombosis. That ad ushered in a whole era of humour, wit and irony in advertising."

VW followed up with the famous "Lemon" ad, which informed car-buyers of VW's process of weeding out bad vehicles, while cheekily nodding at worries that the Beetle itself was a lemon.

Many advertisers followed suit. Perhaps most notably Avis rental cars, whose We Try Harder campaign made a virtue out of their second place position in the US market.

The Marlboro Man

The Marlboro Man certainly wasn't the first iconic advertising figure.

Image caption The Marlboro Man transformed the brand into an ultra-masculine accessory

In 1939, Coca-Cola helped create the modern image of a cheery, rotund, red-outfitted Santa Claus. Before that, representations of St Nick had ranged from skinny and creepy, to stern and downright scary.

Ronald McDonald, like the Marlboro Man, is so recognisable that the product name need not be displayed.

But the Marlboro Man did something more. He transformed the Marlboro brand from a mild ladies' cigarette into a rugged, ultra-masculine accessory.

Unlike Ronald McDonald, men aspired to be the Marlboro Man.

The campaign was wildly successful - Marlboro sales increased 300% in the two years after the ad debuted in 1955.

"There is just a handful of ads ever created that have actually become more important than the product itself, that created wealth and built fortunes," Mr Garfield said.

The Marlboro Man did that through the simple insight that a person's cigarette could speak to his or her self image.

James Twitchell, author of 20 Ads that Shook the World, told the BBC that in addition, the Marlboro Man was an achievement because it found success at a time when Americans were learning that cigarettes were genuinely dangerous, addictive products that could kill you.

"The Marlboro Man was strong, powerful. He never speaks. He's so tough," Mr Twitchell said. "The genius of the ad is that at the same time there was a rising realisation that this thing will kill you, it was identified with a character who was, on the face of it, indomitable."

Sadly, the three actors who played the Marlboro Man died of lung cancer. One sued Phillip Morris and the cigarettes became known colloquially as "cowboy killers".

Nike

In many ways, the differences between pairs of training shoe are marginal. Mr Twitchell calls them fungible, "essentially interchangeable."

Image caption The globally recognized swoosh is one of Nike's advertising successes

But successive savvy advertising strategies turned a little Oregon sports outfitter into the globally dominant sports giant Nike. Their swoosh logo is now one of the most recognizable images on the planet, rendering the actual name unnecessary.

And while Nike may not have been the first company to seek celebrity plugs, its relationship with Michael Jordan is arguably the most successful endorsement in history.

"Nike's great insight was forget the shoe, own the athlete," says Mr Twitchell.

The release of the Just Do It motto in 1988 was a transformative moment for the company, weaving their brand, seemingly forever, with the inspiring and dramatic physicality of sport.

"This was advertising transcending the product. Nike is not a design or a style. It's an idea. They own sport - its passion, its grit," said Mr Garfield.

"They use the same offshore factories and cheap materials as everybody else. But they represent the drama and passion of sport. They just own it."

Absolut Vodka

Image caption Absolut Vodka created a new market (Image courtesy Absolut Vodka)

Like DeBeers, Absolut Vodka's advertising literally created a market where one did not exist.

In 1981, Absolut launched a campaign that would run for nearly three decades using simple ads with prominent images of their distinctive vodka bottle and plays on the word "absolute".

Before that, vodka had seldom been advertised and there was no premium vodka industry.

"Absolut turned a commodity into a badge brand," Mr Garfield said. "They did it on brand name and bottle shape. It was a remarkable visual campaign."

Mr Twitchell agrees.

"Vodka is a hard drink to separate on the basis of taste, so they separated their brand through narrative and package," he says.

These days, premium vodka is an enormous business. Brands like Grey Goose, Ketel One and Chopin owe much to Absolut's pioneering ads.

President Lyndon Johnson

American political advertising is a multi-billion dollar industry these days. Many campaigns have been highly effective, including Ronald Reagan's It's Morning in America campaign or the Republican "Willie Horton" attack ad against Michael Dukakis.

But few campaigns have been as memorable or as devastating as the Daisy ad.

It depicted a young girl playing innocently with a flower in a field. She looks up towards the sky and the camera zooms in on her eye and cuts to a shot of an atomic mushroom cloud.

An announcer urges Americans to vote for Lyndon Johnson because "the stakes are too high for you to stay home".

The ad was chilling and probably unfair, and it paved the way for the modern attack ad.

"It really showed that dirty advertising could produce clear results for the person who could do it well," said Mr Twitchell.

It was also pioneering in a different sense.

The ad was only played once as a paid advertisement by the Democratic National Committee. But it was so controversial it was shown numerous times on news programs and referred to in newspapers and magazines.

The ad was so good it got free publicity - a scenario many campaigns have tried to emulate, but few have actually managed.

Honourable mentions

Image caption Calvin Klein continues to make racy ads

Apple's 1984 ad, directed by film legend Ridley Scott, was screened just once, but it imprinted Apple as what Mr Garfield calls "the heroic insurgent against the looming, evil, tyrannical information Big Brother, which at that point was IBM".

With Macintosh, Apple had created a revolutionary operating system, relying on a mouse and desktop icons. But the ad didn't show a glimpse of either. It simply branded Apple as smashing convention.

In 1980, 15-year-old Brooke Shields sparked controversy when she told audiences in a breathy whisper: "You know what comes between me and my Calvins? Nothing."

The overt sexualization of a young girl in the service of Calvin Klein jeans outraged many Americans, but it also sparked a designer denim craze that persists to this day, and encouraged Calvin Klein to continue to produce racy, provocative ads for decades.

"It was the beginning of the shockervertising plague that befell the Western world for five years," Mr Garfield said ruefully. "Calvin Klein wasn't an advertiser as much as an arsonist."