Perhaps one of the most ethically challenging, and truly heartwrenching, figures of contemporary (by which I mean, post-WWII) philosophy is that of the Muselmann. The word Muselmann literally means "Muslim" ("one who submits to God"), but is used to refer to prisoners of Nazi concentration camps who had become so destitute and dehumanized as to appear like human corpses. Some scholars believe that the term originated from the similarity between the near-death prone state of a concentration camp Muselmann and the image of a Muslim prostrating himself on the ground in prayer. Primo Levi, survivor of the Auschwitz concentration camps and author of Survival in Auschwitz and The Drowned and the Saved employs the figure of the Muselmann in his works to underscore the utter dehumanization of the Nazi genocidal project. Similarly, contemporary Italian philosopher Giorgio Agamben references the Muselmann in his Homo Sacer: Sovereign Power and Bare Life in the process of disambiguating Aristotle's categories of "bare life" (zoe) and qualified, human life (bios).
Like many others, I am deeply troubled by the figure of the Muselmann, both in fact and its use as a philosophical trope. If you're interested, see the emerging debate between myself and the eminently astute AnPan over on his blog at "Interference, Coercion, Domination, Powerlessness."