Here's a copy of a similar figure that I started with, bottom right figure here, dug out again for comparison:
So I worked in GIMP: as you can see I retained the basic shape, belt/lower tunic, eyes, and weaponry. For the beard I clone-stamped lines from the shirt, though I used an eraser brush to carefully taper the line ends a bit which made them look a bit mroe natural to the style. The boot extensions were just black so that was easy (though I clone stamped there too because the black on print is never 100% without white spots). The chainmail was next: for that I spent a while looking at ways that woodcut artists had done chainmail, picked what looked like the simplest option, then digitally erased the lining on the shirt and got to work. I used a bar-shaped paintbrush and just made a lot of individual comma/half-loop shapes by manual mouse drawing, alternating rows in each direction and lining them up as per where the fall of the mail ought to be. That was by far the largest part of the job.
The last part was the helmet, which was simple enough, I first took the top and brim of the hat down a bit, then removed the brim annd hollowed out the remainder. I used the same bar-shaped brush (bar shaped not circular to look more like cuts and pen strokes) to draw a line a bit above the rim, then erased angled bar lines through that to make the helmet studs.