Margret E. Rey, co-creator of the Curious George children's books and a longtime Cambridge resident, died December 21. She was 90.

Rey, who lived on Hilliard Street across from the American Repertory Theater, worked with her husband, Hans A. Rey, on 21 children's books, including seven Curious George stories.

Margret Rey was born Margret Elizabeth Waldstein in Hamburg, Germany in May of 1906. She attended Bauhaus, the Dusseldorf Academy of Art and the University of Munich.

She met her husband in Rio de Janeiro in 1930, where she was working as a photographer. The couple married and moved to Paris, France, in 1936, where Rey worked as a freelance writer and her husband as an illustrator.

The Rey's first collaboration, How the Flying Fishes Came Into Being, was published in 1938. Like the couple's future collaborations, Flying Fishes was written by Margret Rey and illustrated by her husband. The Reys wrote five more books before fleeing Paris by bicycle in 1940, only hours before France fell to Hitler's armies.

The Reys resettled in New York, N.Y., where they continued to collaborate as children's authors.

Curious George first appeared in 1942, and the inquisitive little monkey achieved immediate popularity. The Reys wrote six more Curious George stories before 1966, which together have sold more than 50 million copies worldwide.

The Curious George series has been translated into numerous languages. In France, George is known as "Fifi," while in Denmark he is referred to as "Peter Pedal."

In the mid-1960s, the Reys moved to Cambridge, where Margret has lived since.

Soon after her husband's death in 1977, Margret Rey took a job at Brandeis University in Waltham as an instructor in creative writing.

Rey gave several thousand dollars to Radcliffe-affiliated student groups.

She edited more than two dozen Curious George books between 1984 and 1990, and has adapted many of her stories for film and television.

Last summer, Wordsworth books opened a Curious George children's book store in Harvard Square, only four blocks from Rey's home.

Rey is survived by her sister, Mary Eichenburg of Long Island, N.Y., and her brother, Ludwig Waldstein, who lives in Japan, as well as many nieces and nephews