I'm biased when it comes to Earl Norem's artwork. He might be my favorite illustrator working in paint. Norem wasn't always my favorite, however. When I was young I always thought his work looked dirty. As in, it looked like dirt from the earth was somehow mixed into his paint. I'm not sure how this effect was created. Was he using a palette covered with old paint corrupting the fresh pigment? Was Mars Black getting mixed into his colors? Was the quality of the acrylic back then not very high? Whatever the cause the result is a tonal atmosphere I can't find in many other illustrators' work. Now that I'm older I love the earthiness of Norem's work. When he paints Conan fighting some demon in a crypt, squaring off against a horde of enemy mercenaries in the desert, the dirt feels a part of the air within the world of the paintings. The images feel more real, at least to the logic of the reality presented within the picture plane.
BONUS
All artwork by Earl Norem