"He had a stroke," Hart's wife, Bobby, said Sunday. "He died at his storyboard."
"B.C.," populated by prehistoric cavemen and dinosaurs, was launched in 1958 and eventually appeared in more than 1,300 newspapers with an audience of 100 million, according to Creators Syndicate Inc., which distributes it.
"He was generally regarded as one of the best cartoonists we've ever had," Hart's friend Mell Lazarus, creator of the "Momma" and "Miss Peach" comic strips, said from his California home. "He was totally original. 'B.C' broke ground and led the way for a number of imitators, none of which ever came close."
After he graduated from Union-Endicott High School, Hart met Brant Parker, a young cartoonist who became a prime influence and co-creator with Hart of the "Wizard of Id" comic strip.
Hart enlisted in the Air Force and began producing cartoons for Pacific Stars and Stripes. He sold his first freelance cartoon to the Saturday Evening Post after his discharge from the military in 1954.
Later in his career, some of Hart's cartoons had religious themes, a reflection of his own Christian faith. That sometimes led to controversy.
A strip published on Easter Sunday in 2001 drew protests from Jewish groups and led several newspapers to drop the strip. The cartoon depicted a menorah transforming into a cross, with accompanying text quoting some of Jesus Christ's dying words. Critics said it implied that Christianity supersedes Judaism.
Hart said he intended the strip as a tribute to both faiths.
"He had such an emphasis on kindness, generosity, and patience," said Richard Newcombe, founder and president of Creators Syndicate in Los Angeles.
Newcombe said Hart was the first cartoonist to sign on when the syndicate was created 20 years ago. "Traditionally, comic strips were owned by syndicates," Newcombe said. "We were different because we allowed cartoonists to own their own work. It was because of Johnny's commitment to this idea that made us a success."
Besides his wife, Hart is survived by two daughters, Patti and Perri. He was a native of Endicott, about 135 miles northwest of New York City, and drew his comic strip at a studio in his home there until the day he died.
Funeral arrangements had not been announced.