The term untermensch, which translates from the German as subhuman, was deployed by the Nazis as part of their vicious rhetoric of hatred against those they regarded as inferior, particularly the 'masses from the East' - including Poles, Gypsies, Jews, Russians and Serbs. The term was first used in a racial context by American author Lothrop Stoddard in his 1922 pamphlet The Revolt Against Civilization: The Menace of the Under-man, a diatribe in which the Bolsheviks are described as degenerate imbeciles. Stoddard perhaps consciously posits the term in antithetical relation to Nietzsche's Übermensch, or superhuman, a complex concept not easily summarized, so I'll let someone else do it here! In 1942 the Nazi's distributed a pamphlet entitled 'The Sub-Human' in which they lay out their ideas in somewhat maniacal terms:
The sub-human, that biologically seemingly complete similar creation of nature with hands, feet and a kind of brain, with eyes and a mouth, is nevertheless a completely different, dreadful creature. He is only a rough copy of a human being, with human-like facial traits but nonetheless morally and mentally lower than any animal. Within this creature there is a fearful chaos of wild, uninhibited passions, nameless destructiveness, the most primitive desires, the nakedest vulgarity. Sub-human, otherwise nothing. For all that bear a human face are not equal. Woe to him who forgets it.
At bookmark p361 I briefly discuss Nietzsche's concept of will to power.