"Shadow Devil" was a famous legendary monster. Many years in the past, he had always chosen the northwest part of the Main Plane in which to appear. Green Fog Forest in the southern part of the Ashes Woods was his main base of operations, from which he would occasionally go out to raid and stir up havoc.
This guy mainly did two things: One was raiding villages, killing the residents and turning them into his own shadow soldiers; the other was receiving sacrifices from those followers of evil and granting them poisonous weapons filled with shadow magic.
It went without saying that all of these were bad things.
As for any good things he did… Sorry, but even the most erudite scholar wouldn't be able to think of anything good.
So sticking it with the title of "devil" might have been exaggerating its strength just a bit, but in respect to how evil it was, the name really did fit it perfectly. It didn't paint a false picture at all.