I am curious about when was the first time (novel, tale, paint, drawing, etc.) that the iconic human skull/raven motif was used to refer to the Master of the Macabre, Edgar Allan Poe?
The image of something raven-like (an hour glass with raven's wings, as a symbol of Death) on a skull certainly goes back a long way. Gottfried Wilhelm Sacer made a woodcut of the image in the middle to late 1600s:
As for Poe, certainly the illustrations of Carling and Doré (in specific, those for The Raven) of the mid-late 19th century at least place the raven properly on the bust of Pallas, if not an actual skull.
I think this is one of Carling's creepier ones:
Most of the raven on skull imagery I'm finding appears rather newer, so perhaps not quite the answer you're looking for!