Character Celebrity Endorsement

Companies want to ensure big sales. They won't take any unnecessary risks, so they won't release their products in the crowded, dangerous marketplace without something that will make them stand out. Even the littlest of the gimmicks can work.

Character Celebrity Endorsement occurs when the companies use fictional characters, but celebrities nonetheless (largely cartoon ones) to promote their products, even if the character or franchise featured has nothing to do whatsoever with the product at hand.

Compare Celebrity Endorsement, when real celebrities lend their approval of the product. See also The Dead Rise to Advertise when commercials feature, darkly enough, dead celebrities.

Anime and Manga

 * Bizarrely used in this ad, with Andre and Lady Oscar from Rose of Versailles endorsing the Daihatsu cars' new adjustable seats.
 * Son Goku of Dragon Ball fame appeared alongside his son Gohan and his old pal Oolong in an old eye drops commercial, amongst other old endorsements done around the 80s.

Comic Books

 * Superman endorsed the American Express credit card.
 * And of course there are all those old little comic strip advertisements for Hostess Twinkies starring the likes of Batman, Iron Man, Spider-Man, Aquaman and many more.

Live-Action TV

 * Bob and Doug McKenzie have appeared in several ads over the years, including this Pizza Hut commercial.
 * Kenny Powers supports K-Swiss shoes. This culminated in a series of ESPN the Magazine ads depicting him as the CEO of the company!
 * "Dr." Spaceman for Dr. Pepper as part of the "Doctor's orders" campaign.

Film

 * Will Ferrell's character from Semi-Pro endorsed Old Spice, among others.
 * Austin Powers apparently likes Heineken.
 * The Lorax's film adaptation has about 70 marketing tie-ins all told, one being - of all things - for Mazda SUVs. Something about them being green. One gets the idea that the Powers that be missed the point of the Lorax. A bit.

Music

 * Hatsune Miku appeared in Toyota USA's 2011 Corolla commercials due to the car company sponsoring her then-upcoming concert in Los Angeles, as well as starring in a few mini slice-of-life-esque commercials by the same company.

Newspaper Comics

 * The Peanuts characters have endorsed MetLife insurance since the 1980s.

Video Games

 * Master Chief's brief Game Fuel advertising campaign for Mountain Dew.
 * Regain will make you look 40 years younger just hearing about it. Ask Snake.
 * McDonald's have been known for promoting many Sonic the Hedgehog themed Happy Meals complete with commercials starring the Blue Blur himself (Some of them, that linked video included, even featuring the voice of Ryan Drummond himself at the time.) He's no slouch in the publicity department as we all know, and he even popped up in an advertisement for Progessive Insurance of all things.
 * Lara Croft's known in the UK for, amongst other things, her once frequent endorsement of Lucozade. That linked video is one of many advertisements she did, printed or otherwise.

Western Animation

 * Flintstones vitamin pills.
 * Fred Flintstone and Barney Rubble hawking Winston cigarettes (1961).
 * The Flintstones appear to be really into the commercials, because they also hawk Fruity Pebbles and Cocoa Pebbles.
 * Donald Duck Orange Juice
 * Popeye Spinach (also a form of Defictionalization, since it is his Trademark Favorite Food).
 * Popeye was also used (oddly) to advertise Quaker Oatmeal. "I'm Popeye the Quaker man, I eats all the oats I can!"
 * And let's not forget the Minute Maid ad with extra Foe Yay.
 * Pink Panther (Owens Corning) insulation
 * As well as Safeco Insurance in the late 70s/early 80s.
 * Currently showing in the United States is a GEICO commercial with Elmer Fudd. Here 'tis.
 * They also did an ad with Speed Racer.
 * Bugs Bunny has also gotten in on the action, with ads for Ziploc storage bags (1982), Tang, Kool-Aid and sugar-free vitamins.
 * Jonny Quest was the representative of P.F. Flyers tennis shoes, "The Action Shoes". One can hear Tim Matheson's voice beginning to change in the commercial.
 * The Linus the Lionhearted show was devised completely to flog Post cereals. It featured characters who served as mascots for the various Post cereals, including Linus himself (for Crispy Critters); Lovable Truly, the Postman (for Alpha Bits); So Hi, a little Chinese boy (for Rice Krinkles); Rory Raccoon (for Post Toasties), and Sugar Bear, the only character to survive the show's cancellation (for Sugar Crisp).
 * Bart and Homer Simpson for Butterfinger; this went on for nearly a decade. Homer would later show up in an Intel ad as well. Multiple tie-ins with The Movie may or may not also qualify.
 * Peter Griffin for Subway.
 * And Brian and Stewie for Wheat Thins.