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

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

He was also a novelist and writer.

He is survived by a son and daughter.