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.

At the beginning of his reign, Matt enacts several bold reforms aimed at improving life for the people of his kingdom, especially the children, but in spite of his best intentions, reality gets in the way producing many unintended consequences from silly to sinister.

Matt tries to organize the children of the entire world to hold processions and demand their rights - and ends up antagonizing other kings.

The story is continued in the sequel, King Matt on a Desert Island (Król Maciuś na wyspie bezludnej), published in the same year and translated into English in 1990.

Korczak often employed the form of the fairy tale in order to prepare his young readers for the dilemmas and difficulties of adult life, and the need to make responsible decisions.

The book also makes references to: The author's father died in 1896, leaving Korczak, at 18, the head of the family and the sole breadwinner for his mother, sister, and grandmother.