The Water Spirit (1904).
Theodor Kittelsen is, we’re told, one of Norway’s most popular artists and illustrators. This would explain why so much of his work has appeared on the covers of albums by Norwegian metal bands although it also helps that one of the books he illustrated is entitled Svartedauen (The Black Death). The picture below, one of several portraits of trolls and mythological creatures, appeared on the sleeve of Long Island, the most recent album by US band Endless Boogie. Discogs has a list of Kittelsen’s other album cover appearances which also include classical releases. This site has more of the artist’s paintings and illustrations. (Via Wood s Lot).
Forest Troll (1906).
Fishing Water Spirit (1912).