FORTUNE — A conversation with Joel Ewanick, General Motors’ chief marketing officer for the past ten months, doesn’t proceed for long without his mention of “swim lanes.”

Ewanick isn’t talking about exercise, but his primary task at a resurgent GM . In the 51-year-old executive’s view, his mission is to clearly define the company’s varying brands, taking particular care that, in consumers’ minds, they do not collide with one another — like swimmers separated by lane markers. “We have to develop policies and procedures to this never happens again,” he says. “We want to prevent a repeat of the Fortune cover.”

Ewanick is referring to the August 22, 1983 cover of Fortune magazine (above, right) which has haunted generations of GM executives. It featured four maroon sedans, each from a different GM brand but built on the same engineering platform. All looked identical. The cars’ similarities spoke to consumers’ confusion: how could potential buyers differentiate brands if they couldn’t tell individual models apart? The cover epitomized the company’s mismanagement and the extent to which legendary GM chairman Alfred Sloan’s maxim — a car for every purse and purpose — had been forgotten.

Twenty-eight years later, GM is emerging from another agonizing reorganization. The automaker went bankrupt in 2009 and was rescued and recapitalized by the U.S. Treasury. Storied brands Pontiac, Saturn, Hummer and Saab were shuttered or sold, leaving only Cadillac, Chevrolet, Buick and GMC alive in the U.S. GM was forced to close a dozen facilities and cut more than 20,000 jobs. Perhaps worst of all, GM found itself knocked from its perch as No. 1 automaker worldwide, a devastating blow to already plummeting morale. Now that GM has managed to claw its way back to the top spot, it desperately needs an inspirational marketing leader with an outsider’s perspective.

Enter Ewanick. The hiply-dressed Californian from the San Fernando Valley worked for Porsche, Hyundai and, briefly, Nissan (NSANY) before being recruited by GM President Mark Reuss in mid-2010 to run U.S. marketing. A few months later, GM expanded his portfolio, making him its global chief marketing officer. (In addition to familiar American brands, he is also responsible for the international Holden, Opel and Vauxhall marks.)

So far, he hasn’t eschewed bold moves. He decided to move advertising responsibility for Chevy, which accounts for some 70% of GM’s U.S. sales, to the San Francisco-based agency of Goodby, Silverstein & Partners. Because Detroit-based Campbell Ewald had supervised the account for 91 years, the moved rocked the advertising world. (GM’s global ad expenditure is estimated at a massive $3 billion.)

Campbell Ewald had created arguably some of the most memorable campaigns in automotive advertising history. Classic taglines included “See the USA in a Chevrolet,” “Baseball, Hot Dogs, Apple Pie and Chevrolet,” “Heartbeat of America” and “Like a Rock.” However, when Ewanick took over in May of 2010, the first order of business was to instill new life into GM’s largest brand. He turned to familiar territory — Goodby, Silverstein and Partners. Goodby was Hyundai’s ad agency when Ewanick led its marketing and advertising, and Ewanick has a longtime relationship with agency partner Jeff Goodby. Goodby is known for “Got Milk?,” among other campaigns.

Ewanick wasn’t immediately satisfied though, recently criticizing Goodby’s work as “inconsistent” and ordering up tweaks to its approach. “I can say that we turned the corner,” Ewanick says, pronouncing himself especially pleased with such new Chevy Cruze TV spots as one highlighting a young man’s first date: After giving the young woman a chaste peck one the lips, he gets in his Chevrolet Cruze and pushes the OnStar button. A voice reading his date’s Facebook post says “Best. First. Date. Ever.” GM’s new chief marketing officer likes the “Best Date” ad because he says it’s entertaining, emotional and communicates a specific product attribute, namely the ability of OnStar to audibly recite a Facebook status update to drivers and passengers. (Watch the spot below.)

[youtube http://www.youtube.com/watch?v=vxcKoTZOcA8&w=560&h=345]

Ewanick built his reputation on meticulous execution and unconventional thinking. In the depths of the last recession, he helped to devise the Hyundai Assurance Program, which promised that new-car customers would be protected by insurance in the event they lost their jobs after buying a new Hyundai. It succeeded in raising Hyundai’s profile and market share at a moment when consumer confidence was low.

At GM, Ewanick and team have created “brand books” for Chevrolet and the others, describing for advertisers the qualities and attributes represented by the brand. Chevrolet, for example, is meant to appeal to what Ewanick describes as everyday heroes, a notion that can be adjusted in the respective worldwide markets where Chevrolet is sold. Buick and Cadillac both are luxury brands, though differentiated by physical design as well as type of customer. Cadillac has sharper lines, appealing to an “edgier” personality than softer and smoother Buick. Ewanick calls it a “flanking” strategy that differentiates luxury buyers.

Since the 1983 Fortune cover GM’s US market share has fallen by more than 50%, now hovering around 20%. Similarity of look has been cured — but now the market is flooded with more brands and nameplates than ever, giving consumers unprecedented choice in size, style and price category. Ewanick must take care to avoid the classic mistake of many military strategists, fighting the last war instead of the current one.