"The playful person", a 1938 book by the Dutch historian Johan Huizinga (1872-1945). He coined this term, as against Homo sapiens and other ad-hoc ones like Homo faber (crafting humans), to stress how much the concept of play was central to human exploration of life, and came into our culture, laws, art, science, and so on.

It was one of his last works. He spent his last few years a prisoner of the Nazis. The full title of the book is Homo Ludens: A Study of the Play-Element in Culture.

The spirit of playful competition is, as a social impulse, older than culture itself and pervades all life like a veritable ferment. Ritual grew up in sacred play; poetry was born in play and nourished on play; music and dancing were pure play....We have to conclude, therefore, that civilization is, in its earliest phases, played. It does not come from play...it arises in and as play, and never leaves it.