Many critics have disputed the original source of the Swan Lake story. The Russian ballet patriarch Fyodor Lopukhov has called Swan Lake a "national ballet" because of its swans, who originate from Russian lyrically romantic sources, while many of the movements of the corps de ballet originated from Slavonic ring-dances. According to Lopukhov, "both the plot of Swan Lake, the image of the Swan and the very idea of a faithful love are essentially Russian". The libretto is based on a story by the German author Johann Karl August Musäus, "Der geraubte Schleier" (The Stolen Veil), though this story provides only the general outline of the plot of Swan Lake. The Russian folktale "The White Duck" also bears some resemblance to the story of the ballet, and may have been another possible source. The contemporaries of Tchaikovsky recalled the composer taking great interest in the life story of Bavarian King Ludwig II, whose tragic life had supposedly been marked by the sign of Swan and who—either consciously or not—was chosen as the prototype of the dreamer Prince Siegfried.