Call them whatever you want: celebrity spokespeople, brand ambassadors or product pitchmen. Over the years, they've all been used to varying degrees and resulting levels of success by marketers and agencies to accomplish the same things -- provide a point of differentiation against similar products, communicate product benefits in memorable ways, and provide an "accessible" human voice for corporate-sounding brands.

As a kid, I remember watching the likes of O.J. Simpson running through airports for Hertz; Anita Bryant opining on orange juice for the Florida Citrus Commission; James Garner and Mariette Hartley pitching for Polaroid; Joe DiMaggio preaching the perks of Mr. Coffee; Brooke Shields slipping into her Calvin Kleins; and Karl Malden never leaving home without his American Express card.

And while I may have been too young at the time to rent a car from Hertz, buy a camera from Polaroid or apply for an account with American Express, I remember the advertising for those brands nearly 40 years later much more than I do for any of their competitors.

On the surface, these endorsement relationships seem to make perfect sense: Get consumers to favor your brand by partnering with their favorite celebrities or sports stars. What's not to like? Why wouldn't every marketer use them, knowing their potential and promise for brand differentiation and increased sales?

But any advertiser or marketer can tell you it's not that simple. In fact, for every successful product pitchman, there are plenty of examples of endorsements gone wrong.

You can bet Hertz regrets its run with O.J. and that Jell-O would like to swallow and forget its Bill Cosby affiliation. No doubt that Nike had second thoughts about Tiger Woods and Kobe Bryant, even though both maintain relationships with the brand today.

And now there's the case of Subway and Jared Fogle. Perhaps the most successful endorsement deal in the history of marketing came crashing down earlier this summer following the child pornography and sex with minors allegations made against Fogle. Subway, of course, had no choice but to end its 15-year partnership.

Ever since Fogle lost 200 pounds in college, thanks to a Subway-centric diet, he's been intrinsically linked to the sandwich chain, helping it to grow to 44,000 locations around the world. In fact, Subway credits Fogle and his advertising campaigns with between one-third and one-half of the sandwich chain's sales increases during his time with the company.

Ironically, Subway made Fogle a celebrity. He was an unknown from Indiana when his first commercial aired in 2000. Until recently, he's been the face of the brand and has been associated with it just as much as its foot-long sub or yellow and green logo.

And while Subway will undoubtedly introduce a new Jared-less advertising campaign (the company has tapped BBDO to take over creative duties and has been reassessing its overall marketing approach), it will forever be linked to Fogle by a generation of consumers who watched more than 300 commercials featuring him endorsing the brand over the past decade and a half.

Yet, even with the perils of product pitchmen, brands and agencies seem addicted to the appeal of "endorsement marketing."

Tom Brady's association with Under Armour has likely caused some discomfort, thanks to his involvement with the "Deflategate" scandal that's dominated sports news for the past seven months. Whether Brady's guilty or not isn't the point. Under Armour is interested in Brady's performance on the field, winning NFL championships and MVP awards. The last thing it needs is an association with a player who's suspended from playing because of allegedly cheating.

And who knows what the future will bring with regard to other celebrity controversies on or off the stage, golf course or basketball court? Thanks to the proliferation of smartphones and tablets with cameras and recording devices, it's undoubtedly more difficult to remain squeaky clean in the public's eye today than it was when the likes of Mickey Mantle, Joe Namath or Marilyn Monroe dominated pop culture.

Nothing seems to remain private these days, and that's why celebrity endorsements are riskier than ever. The payoffs can be huge (witness Michael Jordan's phenomenally successful association with Nike). But when they go bad, the costs are immeasurable and the brand damage is difficult to overcome.

Don't be surprised if Subway's next campaign features a talking sandwich, or a mascot that is sure to never embarrass the company.