W. Watts Biggers, who with a partner created the 1960s cartoon “Underdog” as a way to sell cereal and wrote its infectious theme song, died on Feb. 10 at his home in Manomet, Mass. He was 85.

The cause was a heart attack, Nancy Purbeck, his longtime companion, said.

Mr. Biggers was an account manager at the advertising firm Dancer Fitzgerald Sample in the early 1960s when he and Chet Stover, a copywriter, began conceiving a cartoon show to advertise General Mills cereals.

Mr. Biggers and Mr. Stover talked over dozens of ideas, but nothing seemed right. They knew that they would be competing for a morning time slot with Jay Ward and Bill Scott, who had created “Rocky & Bullwinkle.”

“We were going to be the underdog,” Mr. Biggers recalled saying to Mr. Stover. The idea stuck, giving birth to Underdog, a humble shoe shiner who would be transformed into a superhero, especially whenever the reporter Sweet Polly Purebred was threatened. It won the slot and made its debut on NBC in 1964.

Voiced by the character actor Wally Cox in rhyming couplets, Underdog battled villains like the evil scientist Simon Bar Sinister and the wolf gangster Riff Raff. Underdog’s segments on the show were interspersed with those of other cartoon characters like the Go Go Gophers and Tennessee Tuxedo.

“Underdog” proved so popular that Mr. Biggers and Mr. Stover left advertising to start a production company, Total Television, with Joe Harris and Treadwell Covington. They wrote more than 100 episodes of “Underdog,” and Mr. Biggers, the composer of the group, wrote the theme music for the company’s cartoons. (He also credited his partners Mr. Stovers, Mr. Harris and Mr. Covington.)

The show is syndicated worldwide, and an Underdog balloon has appeared in the Macy’s Thanksgiving Day Parade. A live action movie based on the cartoon, starring Jason Lee as the voice of Underdog, was released in 2007.

The theme song (beginning, “There’s no need to fear! Underdog is here!”) pops up in unexpected places. The Blanks a cappella group performed an extended version of the song on the sitcom “Scrubs,” and the hip-hop artist RZA sampled it on the album “Enter the Wu-Tang (36 Chambers.)”

William Watts Biggers was born on June 2, 1927, in Atlanta to Rosemary and Bascom Biggers, a big band leader. In addition to Ms. Purbeck, Mr. Biggers is survived by a daughter, Victoria; a son, W. Watts Jr.; a brother, Bascom III; Ms. Purbeck’s children, Andrea Condon and Jeffrey Turgeon; and Ms. Purbeck’s four grandchildren. His wife of 39 years, Grace, died in 1989.

Mr. Biggers went to work for NBC in the late 1970s and left in 1984 to focus on writing.