Dick Bruna, a Dutch children’s author and illustrator who was celebrated for the simplicity of his depictions of Miffy, a white rabbit who has delighted preschoolers the world over for six decades, died Feb. 16 in Utrecht, the Netherlands. He was 89.

The death was announced on his website. The cause was not disclosed.

Mr. Bruna published 124 picture books that sold more than 85 million copies in more than 50 languages. But his best-known volumes were those featuring Miffy, the bunny who debuted in 1955 and was thereafter immediately identifiable for her tall ears, her two dots for eyes and her “X” in place of a mouth.

Known in Dutch as "Nijntje," Miffy joined Babar the elephant (created by Frenchman Jean de Brunhoff in 1931) and was soon followed by Paddington Bear (introduced by Englishman Michael Bond in 1958) in Europe's pantheon of literary animals. Beyond the continent, she ranked among the most popular Dutch exports, a commodity as valuable to publishers as she was beloved among toddlers.

The hallmark of Mr. Bruna's books was their purity. His stories followed Miffy through experiences such as a visit to the zoo, a romp through the snow and a trip to the hospital. In his artwork, he favored simple lines and solid colors, distilling the shapes of the world to what he described as their "essence," with room left over to let the child's imagination run.

To an undiscerning eye, the style may have belied his genius.

"Stare at Miffy head on," Kathryn Shattuck, a culture writer, once observed in the New York Times, "and Mr. Bruna's sculptural training becomes evident as the figure's straightforward unshaded body, outlined in firm ink strokes, assumes rounded proportions, colored in the primary hues favored by Mondrian and Matisse, two of his inspirations."

In 2015, when Miffy turned 60, she was feted with an exhibit at the Rijksmuseum in Amsterdam. Speaking to the London Independent that year, a Dutch fashion illustrator, Piet Paris, commended Mr. Bruna for the "almost Zen-like" nature of his creations.

Mr. Bruna displayed little interest in art criticism or marketing strategies, although the Miffy series — which came to include television shows, a movie, clothing, stuffed animals and other merchandise — was a resounding business success. He professed that his goal was simply to create books that children would enjoy.

“I sometimes think children are looking on from the other side of my table when I am drawing,” he once said. “They always look straight at you, it is a matter of honesty. That’s why Miffy also faces the onlooker directly.”

The books were square-shaped, roughly 6 inches by 6 inches, to better fit tiny hands. With the subtlest alterations to Miffy’s only facial features — the two dots and an X — he conveyed a universe of emotion. One volume explored Miffy’s feelings upon the loss of her grandmother.

“I thought that if there is someone who can tell children about a thing like death, then maybe it is Miffy,” he told the London Daily Telegraph. “I always said I would tell no fairy tales with her; she does the things that children do. The death of a relative is just another normal childhood experience.”

Hendrikus Magdalenus Bruna was born in Utrecht on Aug. 23, 1927. He began drawing as a diversion during the German occupation of World War II, when his family went into hiding at a lakeside retreat to protect his father, a publisher, from conscription intoforced labor.

After the war, Mr. Bruna apprenticed at the W.H. Smith bookstore in London and the Plon publishing company in Paris. He also studied at the Rijksakademie in Amsterdam before joining his family’s firm, A.W. Bruna & Zoon.

Mr. Bruna distinguished himself designing book covers and posters before devoting himself to children’s writing full time. His first book was “The Apple” (1953). Two years later he created Miffy after he and his young son encountered a playful rabbit during a seaside vacation. The rabbit was of undetermined gender until 1963, when Mr. Bruna drew her for the first time wearing a dress.

He evinced distaste for Hello Kitty, the Japanese brand launched in 1974. The sparsely sketched white cat was, in his eyes, a copy of Miffy.

“I don’t like that at all,” he told the Telegraph. “Try to make something that you think of yourself. After all . . . there’s so many nice things.”

Mr. Bruna’s survivors include his wife, Irene de Jongh, whom he married in 1952; two sons, Sierk and Marc; a daughter, Madelon; and six grandchildren.

Beyond his book writing, Mr. Bruna accepted commissions from UNICEF, the Red Cross and Amnesty International.

Looking back on Miffy, he said he hoped she had sparked the imaginations of young readers “to see things in their simplest form.”

"So that life, with all its complications," the Times quoted him as saying, "becomes a little clearer."