What impact did Hans Christian Andersen have on children’s literature?

Oxford Dictionaries:

An extract from the Oxford Encyclopedia of Children’s Literature, available on Oxford Reference.

Although Andersen considered himself a novelist and playwright, his novels, dramas, and comedies are almost forgotten today, while his unquestionable fame is based on his fairy tales. He published four collections: Eventyr, fortalte for børn (Fairy Tales, Told for Children, 1835–1842), Nye eventyr (New Fairy Tales, 1844–1848), Historier (Stories, 1852–1855), and Nye eventyr og historier (New Fairy Tales and Stories, 1858–1872), which were an immediate, unprecedented success and were translated into many languages during his lifetime. Yet only a handful of his fairy tales and stories are widely read today.

Sources of his stories: from folklore to literature

Although Andersen could have read Grimms’ fairy tales, the sources of his stories were mostly Danish folk tales, collected and retold by his immediate predecessors J. M. Thiele, Adam Oehlenschlæger, and Bernhard Ingemann. Unlike the collectors, whose aim was to preserve and sometimes to classify and study folktales, Andersen was primarily a writer, and his objective was to create new literary works based on folklore, although some of his fairy tales have their origins in ancient poetry (“The Naughty Boy”) or medieval European literature (“The Emperor’s New Clothes”). He also found inspiration in the literary fairy tales by the German Romantics such as Heinrich Hoffmann and Adelbert von Chamisso.