Karl Wilhelm Diefenbach (21 February 1851 in Hadamar – 15 December 1913 in Capri) was a German painter and social reformer.
Diefenbach is regarded as the "forefather of alternative movements" and one of the most important champions of the Lebensreform (life-reform), the Freikörperkultur (naturism) and the peace movement. His rural commune Himmelhof, in Ober Sankt Veit near Vienna (1897–1899) was the model for the reform settlement Monte Verità near Ascona, founded by his student Gustav Gräser, who is also known as the "Grail of Modernity". As a painter, Diefenbach was an independent representative of symbolism.
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