Der kleine König Macius. Eine Geschichte in zwei Teilen für Kinder und Erwachsene.

King Matt the First (Polish: Król Maciuś Pierwszy) is a children's novel by Polish author, physician, and child pedagogue Janusz Korczak. In addition to telling the story of a young king's adventures, it describes many social reforms, particularly targeting children, some of which Korczak enacted in his own orphanage, and is a thinly veiled allegory of contemporary and historical events in Poland. The book has been described as being as popular in Poland as Peter Pan was in the English-speaking world. It was the first of Korczak's novels to be translated into English – several of his pedagogical works have been translated, and more recently his novel Kaytek the Wizard was also published in English.