kicking off with *drumroll* - Dolcett.
I don't know about "best guro artist of all time", that's very subjective.
Dolcett is kind of the "grandfather" of modern gore. At the very least one of them.
A bunch of other great artists have been influenced by his work, often doing tributes.
His work has been around for decades. For the most part working with B&W drawings, his themes span from often
spitting & roasting, cannibalism, cooking alive, beheading, lots of hanging, shootings, drowning, electrocution and some select hints of vore to flaying and more.
A lot. Most of the times lovingly and with a wink of good humor.
B&D Pleasures sold his art prints during the 1980s, but his fame really took flight with the birth of the internet.
He did a lot of comics and whole stories, so sticking to the "around 5 images per artist" suggestion, I merged some of his works to keep parts of the story intact.
Still, picking 5 out of about 500 is not an easy task and a very personal choice, of course.