BOSTON (AP) — William Watts Biggers, the co-creator of the cartoon "Underdog," the mild-mannered canine shoeshine boy who turned into a caped superhero to rescue his girlfriend, Sweet Polly Purebred, has died. He was 85.

Family friend Derek Tague says Biggers, who went by "Buck," died unexpectedly at his Plymouth, Mass., home on Sunday.

The native of Avondale Estates, Ga., worked for the New York City advertising firm DFS when he accepted an assignment from the agency's largest client, General Mills, to create television cartoons to promote its breakfast cereals. The most famous was "Underdog," which debuted on NBC in 1964.

The canine superhero, voiced by comic actor Wally Cox, also battled villains including mad scientist Simon Bar Sinister, and a gangster wolf Riff Raff.

Upon hearing the cries of Sweet Polly Purebred, Underdog would rush into a telephone booth and transform into the hero.

He spoke in simple rhymes, his most famous probably "There's no need to fear, Underdog is here."

Biggers also helped create "King Leonardo and His Short Subjects" and "Tennessee Tuxedo and His Tales."

After General Mills pulled out of the animation business, Biggers became vice president of promotion and creative services at NBC.

The family said Biggers "delighted in the enduring appeal of his 'Underdog' franchise," including the balloon that appeared in the Macy's Thanksgiving Day Parade, and the 2007 live-action film.

Biggers also wrote for publications including TV Guide, Family Circle and Reader's Digest, and wrote several novels, including "The Man Inside" and "Hold Back the Tide."

Biggers' wife of 39 years, Grace, died in 1989. He is survived by his daughter, Victoria Biggers, his son, W. Watts Biggers, Jr., and longtime companion Nancy Purbeck.

Funeral arrangements will be private. A memorial service is planned for a later date.