Brace yourself adland: The Jolly Green Giant and Cheerios Kid are on the comeback trail.

General Mills is resurrecting the classic characters in two new ad campaigns debuting Monday that will make a nostalgic appeal to convince consumers of the health benefits of the iconic cereal and vegetable brands.

The Giant, who debuted in 1928, will return to take a prominent role in a TV ad for the first time in some eight years via a campaign that marks the beginning of a revival for the big fella. In recent years, the giant had been relegated to low-profile appearances, appearing only as a shadow in some spots. Stuck in a standing position for decades, he will transition from a protector of the land to a kind-friendly "wingman" for parents to help make healthy eating fun, said Yumi Clevenger-Lee, marketing manager for the Giant brand. On Facebook and at an augmented-reality event in New York City in October, he will ask kids to take "One Giant Pledge" to eat one more vegetable a day. "We're bringing the jolly back to the Green Giant and helping him get his mojo back," she said.

While less known, the animated Cheerios Kid was famous in his day, appearing in TV ads in the 1950s and 1960s, encouraging kids to "connect the 'Big G to the Little O' to get the 'Go' power of Cheerios." In the new campaign he will speak to nostalgic Baby Boomers in an online video in which he gives a scientific explanation to longtime sidekick Sue about how eating Cheerios can "help naturally remove some cholesterol from the body." The spot (below) will initially run on YouTube, Facebook and WebMD.

"He was a very powerful character in his day," said Meredith Tutterow, associate marketing director for Cheerios. "So we thought wouldn't it be fun to get the Cheerios Kid to help educate these friends of his from 30 years ago, now all grown up, and help teach them about how Cheerios can help lower cholesterol."

General Mills made the Giant TV ad in-house, while Story Worldwide is handling digital and PR is by Olson. The Cheerios video was handled by Pat-Man Studios. The creative agency for both brands is Saatchi & Saatchi.

Both campaigns are an example of how iconic brands -- from Starkists' Charlie the Tuna to Alka-Seltzer's baby-faced Speedy -- are bringing back old characters in new ways, often using digital media create rich storylines not possible in the past.

The Green Giant was created in the 1920s by the Minnesota Valley Canning Co. and was named after a "variety of particularly large peas," according to the brand's web site. Originally hunched over and frowning, he evolved over the years into a greener, happier giant. One of his caretakers was Leo Burnett, who had the brand as one of his first clients when he opened the agency that bears his name in 1935. Minnesota Valley renamed itself Green Giant Co. in 1950, and was sold to Pillsbury in 1979. In 1999, Ad Age ranked the Giant as the No. 3 ad icon of the 20th Century, trailing only the Marlboro Man and Ronald McDonald.

But General Mills, which acquired Pillsbury in 2001, has "underleveraged him over the years," Ms. Clevenger-Lee said. On packaging, the giant shrank and in one recent TV ad, he appears only as a shadow formed over a farm field, as a ghostlike "Ho,ho,ho," closes the spot. Ms. Clevenger-Lee is on a mission to bring him out of the Valley and make him a star again, calling it "every marketer's dream to have such a powerful icon."

In the new TV spot, his green, smiling face sings the song at the end of an ad showing children taking the veggie pledge and steers viewers to a newly revamped Facebook page where they can interact with him, while taking the pledge. Fans can sign up to get personalized text messages from the Giant, or download "Ho, ho, ho" ringtones. On October 2 at Grand Central Terminal, the brand will use augmented reality to let children with a life-sized version of the icon displayed on a giant screen. And this is just the start: Saatchi & Saatchi is working on a broader campaign, called "Unleash Your Inner Giant," that will continue to evolve the character.

The Cheerios Kid's return comes as the yellow-boxed brand seeks to renew its emotional connection with consumers. The brand's main campaign, which debuted this summer on TV, revives the 'One and Only Cheerios' jingle that was rewritten and sung by Bess Rogers, whose version was picked from more than 80 entries.

The song is meant to recapture the notion that "Cheerios are part of so many special moments," said Ms. Tutterow, noting that she, like many mothers, fed her children the cereal when they were babies. "There's something very precious for moms about that first food moment."

The Cheerios' Kid spot sticks to a more functional message of cholesterol health. While the brand has been pushing that message for a while, the spot seeks to explain the science behind it because consumers "didn't really know how it worked," Ms. Tutterow said.

In 2009, General Mills got into some trouble with the Food and Drug Administration for a similar health claim in which it said the cereal could "lower cholesterol 4% in six weeks." The FDA, in a controversial ruling, warned that the claim was incorrectly promoting the cereal as a drug. The brand quietly removed the claim, replacing it with the more vague "can help lower cholesterol." A footnote states that 3 grams of soluble fiber from whole-grain-oat foods "like Cheerios" in a diet low in saturated fat and cholesterol "may reduce the risk of heart disease."

The agency closed the case in May.