Jan Pienkowski, the children’s book author and illustrator known for his innovative, painstaking design, has died at 85, the Guardian reports.

Pienkowski was born in Poland and became a refugee, with his family, when World War II broke out in 1939. After living in a series of countries in Europe, Pienkowski’s family moved to England when the author was young.

He worked for a greeting card company before turning his attention to children’s books in the late 1960s. In 1971, he won the Kate Greenaway Medal, a British award for illustration in young people’s literature, for The Kingdom Under the Sea and Other Stories, written by Joan Aiken. He won again in 1979 for Haunted House.

His recent books include Botticelli’s Bed & Breakfast, The Fairy Tales, and The Glass Mountain.

Pienkowski’s admirers remembered him on Twitter. “RIP Jan Pienkowski, whose books…are front and centre of my childhood memories,” wrote illustrator Rob Biddulph. “I was always so happy when Mrs Harris would read them at storytime. Some books really do leave an indelible impression, and I’m so grateful.”

And author/illustrator Ed Vere tweeted, “One of the true greats of children's books. Jan Pienkowski gave so much to the world. Absolutely brimming with wit and joy...he was a delight! He will be much missed.”

Michael Schaub is a Texas-based journalist and regular contributor to NPR.