Keane died Tuesday of congestive heart failure at his longtime home in Paradise Valley, Ariz., according to King Features Syndicate, which distributes the daily comic.
The first cartoon appeared in 19 newspapers on Feb. 29, 1960. It is a drawing of a census taker who inquires of a puzzled woman surrounded by a roomful of toys: "Any children?"
"The Family Circus" appears in nearly 1,500 papers around the world today, making it the most widely read syndicated panel, according to King Features.
"He was so marvelous. I always felt that he had a great sense of truth," said Mell Lazarus, creator of the "Momma" comic strip. "He had a vivid imagination. It's one of those cannot-miss features."
The strip's characters remained largely the same age year in and year out — an ageless suburban mother and father and their four children, Billy, 7; Dolly, 5; Jeffy, 3; and PJ, 18 months. The daily panels were routinely drawn within a circle, which underscored their sense of closeness, according to the syndicate.
Like many humorists, Keane mined his own family for material. He admitted to modeling the bespectacled and often befuddled Daddy on himself. His wife, Thelma, was the inspiration for the always-loving and ever-patient mother, also named Thel.
"When the cartoon first appeared, she looked so much like Mommy," Keane told the Associated Press after his wife died in 2008, "that if she was in the supermarket pushing her cart, people would come up to her and say, 'Aren't you the Mommy in "Family Circus?"'"
The children in the strip were largely composites of his own five, but PJ "is the best of all my children: cute, usually smiling, once in a while naughty," Keane told the San Jose Mercury News in 2004.
In one cartoon, Jeffy tells a friend: "His name is PJ — but most of the time, he's called No-No."
"I don't just try to be funny," Keane told The Times in 1990. "Many of my cartoons are not a belly laugh. I go for nostalgia, the lump in the throat, the tear in the eye, the tug in the heart."
"The Family Circus" plugged in to the universality of the family experience, and readers related, said Andrew Farago, curator of the Cartoon Art Museum of San Francisco.
"Kitchens coast to coast have 'Family Circus' strips cut out of the newspaper on them," Farago said, "because you will be reminded of something that your sister did or what your father said at breakfast."
William Aloysius Keane was born Oct. 5, 1922, in Philadelphia to Aloysius William and Florence Keane and grew up in suburban Crescentville, Pa.
Self-taught as an artist, he started out imitating the style of New Yorker cartoonists in the late 1930s. After Keane drew cartoons for four publications at his parochial high school, he realized that he had found his life's calling, he later said.
His parents could not afford to send him to art school, so after high school he worked as a messenger at the Philadelphia Bulletin newspaper — and observed the staff artists.
While putting out a satire magazine, the Saturday Evening Toast, with a group of friends in the late 1930s, he changed the spelling of his first name to "Bil" because the other artists on the project were altering their names.
He spent three years in the Army during World War II, drawing for Yank magazine and the Stars and Stripes newspaper. Keane also sold cartoons to a national magazine and met his future wife while stationed in Brisbane, Australia, where they shared office space. He married the native Australian in 1948.
From 1945 to 1958, he was a staff artist for the Philadelphia Bulletin and continued to free-lance as a cartoonist.
In 1954, he launched a syndicated comic strip, "Channel Chuckles," that lampooned the burgeoning medium of television. In one strip, a mother holds a bawling baby in front of the TV as she explains to the father: "She slept through two gun fights and a barroom brawl — then the commercial woke her up."
At its peak, "Channel Chuckles" was syndicated in more than 200 papers before Keane retired the strip in 1976.
After a decade in Roslyn, Pa., the Keane family moved to Arizona in 1958 because of Bil's allergies. Working at home as a free-lance cartoonist, he realized that most of his humor revolved around family life and small children, he later said.
Two years later, he started drawing the comic that was originally called "The Family Circle." When the magazine of the same name objected, Keane changed the second word to "Circus."
For decades, his youngest son, Jeff, has worked with Keane on "The Family Circus" and will continue the cartoon. Another son, Glen, is an animator best known for his work at Disney.
Keane created three animated specials for television and published more than 40 books. In 1971, he collaborated with his neighbor, family-humor columnist Erma Bombeck, on "Just Wait Till You Have Children of Your Own!"
In the foreward to another Keane book, Bombeck wrote: "Mostly I admire and respect Bil's gentleness, his warmth, his respect for that battered, floundering, much-maligned institution — the American family."
Among fellow cartoonists, Keane was known to display a hard-edged sense of humor that Lazarus described as "sardonic." Keane softened his approach for the comic strip, aided by a "tremendous memory" that made it easy to come up with ideas, he later said, and perhaps to continue to see the world through the eyes of a child.
In one panel of "The Family Circus," Jeffy holds a snapshot of his father as a boy and asks, "Mommy, when did Daddy get little?"
Keane is survived by his five children, Gayle, Neal, Glen, Christopher and Jeff; nine grandchildren and one great-grandchild.