Bwonsamdi is inspired by Baron Samedi, a figure in Haitian Voodoo
Wikipedia: He is usually depicted with a top hat, black tail coat, dark glasses, and cotton plugs in the nostrils, as if to resemble a corpse dressed and prepared for burial in the Haitian style. He is frequently depicted as a skeleton (but sometimes as a Black man that merely has his face painted as a skull), and speaks in a nasal voice.
Edit: Sorry, it was just Bwonsamdi, not Ryuk