Dr. Harrow appears in one issue of the "Moon Knight'' comics, as a Nobel Prize-nominated researcher who specializes in pain tolerance. In the comic, it’s uncovered that he uses human test subjects against their will, with experiments inspired by Nazi researchers.
However, there seems to be some distinct differences between the villain from the comics and the one played by Ethan Hawke. The new iteration of Dr. Harrow will be a cult leader (sans the facial paralysis detailed in the comics) with legions of fans bowing to his whims.
It’s possible Dr. Harrow will lead the Cult of Khonshu, the Egyptian deity who gives Moon Knight his powers. After all, Dr. Harrow encourages Marc Spector to "embrace the chaos," so perhaps he wants to use the next iteration of Khonshu for his own nefarious ends.