Der Wächter des Seins

Recently promising myself to sketch fairly regularly, I never imagined that I'd feel the need to illustrate certain concepts intrinsic to the historical-philosophical destiny of the West (specifically, its conclusion). Yet, a number of photo illustrations later (here and here), I've decided to conflate two related concepts--the night watchman from Nietzsche and the guardian of Being from Heidegger--into a single conté sketch. A personification, of course. 

"I had turned my back on all life, thus I dreamed. I had become a night watchman and a guardian of tombs upon the lonely mountain castle of death. Up there I guarded his coffins: the musty vaults were full of such marks of triumph. Life that had been overcome looked at me out of glass coffins."
(Nietzsche describing Zarathustra's dream)

Can you guess who was the source for this image?