(b Adelbye, nr Flensburg, 25 July 1865; d Berlin, 15 Nov 1944). German painter. After training at the Gewerbe- und Kunstschule in Hamburg (1884–9), he attended the Königlich-akademische Hochschule für Bildende Künste in Berlin. His work on the Berliner Dioramen in the late 1880s helped him to further his knowledge of depicting illusionistic states of colour and light. In the 1890s, at first in response to the influence of Fritz von Uhdes’s socio-religious themes, Dettmann initially joined the Secession movement. His exploration of purely pictorial objectives became more important to him. He endeavoured to combine subject-matter, the immediacy of his visual impressions and atmosphere into a unified whole. A result of this phase is Princess and Swineherd (1896; Kiel, Christian Albrechts-U., Ksthalle), the subject taken from a fairy tale by Hans Christian Andersen. More importance was given to the woodland scene drenched in sunlight than to the two protagonists in the painting. From 1900 Dettmann concentrated on paintings that identified with the Fatherland. Tomorrow Is a Holiday (1900; Kiel, Christian Albrechts-U., Ksthalle) shows his attempts to fulfil a thematic objective by applying his own pictorial principles. His identification with the Fatherland led him to espouse the racist theory of culture that was developing in Germany at that time, which restricted his vision for artistic development.