Berenstain died Friday after a stroke in Solebury, Pa., according to HarperCollins, her publisher.
Some 300 titles and 260 million copies later, the series featuring bumbling Papa Bear, practical Mama Bear and their children, Brother and Sister Bear, who live together in a multi-story treehouse, still resonates in families with pre-schoolers.
"The themes of those books — being kind to others, treating people with respect, being nice to your friends, saying what you mean — are universal," said her editor, Dave Linker. "They brought a lot of humor, so reading them didn't feel like drudgery."
Berenstain was instrumental to the collaboration. Both she and her husband, who died in 2005 at 82, were accomplished illustrators and worked together on nearly every book. He was responsible for most of the humor and she for the stories' "heart," Linker said.
Both Berenstains acknowledged that they endowed their alter egos with their own character traits. Papa Bear provides comic relief, often behaving as foolishly as his offspring, while Mama Bear is the voice of reason and morality who guides everyone to a tidy solution.
"I hate the Berenstain Bears," syndicated columnist Charles Krauthammer wrote in 1989. He found Papa Bear so wimpy "he makes Dagwood Bumstead look like Batman." As for Mama Bear, he wrote, "Every adult will recognize her as the final flowering of the grade-school prissy.… The one you always dreamt of drowning."
Mama, Berenstain acknowledged in a Washington Post interview many years ago, "is based on me. But I'm not as nice or stalwart."
Born Janice Grant in Philadelphia on July 26, 1923, she met Stan in a first-year drawing class at the Philadelphia Museum of Industrial Art in 1941. During World War II, he served in the Army as a medical artist, while she completed her studies at Philadelphia College of Art and worked as a riveter in a factory assembling flying boats for the military.
They were married in 1946, a few weeks after Stan's discharge, and began collaborating on cartoons for the Saturday Evening Post and Colliers. They found success with domestic humor, finding something laughable in burnt dinners and squabbles over who used up the toothpaste.
By 1956, they were the parents of two boys, Mike and Leo, and began drawing a monthly feature for McCall's magazine called "It's All in the Family."
In the early 1960s, spurred by their sons' love of Dr. Seuss books, they decided to try writing and illustrating a children's book. They took the story about a family of lovable, human-like bears to Dr. Seuss himself, Theodor Geisel, who was editor-in-chief and president of Beginner Books, a division of Random House.
Geisel provided crucial input. He shortened the authors' first names so they rhymed. Thus, Stanley became Stan and Janice Jan.
To sharpen the characters, he asked them to model the bears on actors. So the Berenstains based Papa's personality on Wallace Beery, who played the down-on-his-luck boxer in "The Champ," while Brother was based on Jackie Cooper, who played the devoted son in the sentimental 1931 classic movie.
Written in rhyme, the story about the bears' quest to replenish the family honey pot was published in 1962 as "The Big Honey Hunt." Still in print, it begat an enterprise that has branched out into chapter books for older readers, animated TV specials, Saturday morning cartoons, clothing, toys, video games, even an iPhone app.
After Stan's death, Berenstain continued to produce books with son Mike, who will run the family enterprise with his brother. Nineteen new Berenstain books will be published this year.
Naming the bears after themselves was not the Berenstains' idea. It was Geisel's. After he accepted their second book, "The Bike Lesson," he added a line to the cover calling the story "Another adventure of the Berenstain Bears."
"That's really how our bears were named," Berenstain told an interviewer for Something About the Author. "We never really would have thought of it."