Paul Adolf Hauptmann (1887-1958). German painter.
I am sorry for the bad quality of the image, I could not find another one. It is not so common for an artist to represent himself naked, all the more assuming this pose with hands on hips. Yet this painter very little known to the public has had the courage to do it, yes, because it is courage and nothing else. What can we say? Plagued as we are by so many exhibitionists and charlatans we should just thank him.