Leo Dillon, who with his wife and longtime collaborator, Diane, was one of the world’s pre-eminent illustrators for young people, producing artwork — praised for its vibrancy, ecumenicalism and sheer sumptuous beauty — that was a seamless amalgam of both their hands, died on Saturday in Brooklyn. He was 79.

The cause was complications of surgery for lung cancer, according to the Dillons’ publisher, Scholastic, which announced the death.

The Dillons, who met in art school, became instant archrivals and remained together from then on, won two Caldecott Medals, considered the nation’s highest honor for children’s-book illustration.

The first, in 1976, was for “Why Mosquitoes Buzz in People’s Ears,” a West African folk tale retold by Verna Aardema; the second, in 1977, was for “Ashanti to Zulu: African Traditions,” by Margaret Musgrove.