Jean-Michel Nicollet: Book covers
One of the most memorable and accomplished of the French artists contributing to Heavy Metal / Metal Hurlant in the late 70s and early 80s was Jean Michel Nicollet.
His distinctive style is showcased at this website, 'Neo' (the acronym for 'Nouvelles Editions Oswald'), which provides images of French paperbacks for which Nicollet did the cover art.
I'm not fluent in French, but I gather that Neo is a specialty publisher in the 'fantastique' genre. The paperbacks, all of which were issued in the 70s and 80s, reprint famous works of fantasy, sf, and mystery genres. Represented are well-known authors like Robert E. Howard, Clark Ashton Smith, William Hope Hodgson, and Brian Lumley, among others.
Also receiving cover artwork from Nicollet are some of the 'Harry Dickson' ('The American Sherlock Holmes') novels by the Belgian author Jean Ray.
[Nicollet apparently ia a big fan of the Harry Dickson stories, which remain tremendously popular in Europe but sadly, have never been widely translated into English, and given the wide dispersion for US consumption that they deserve.]
Unfortunately, those few Neo editions that are available from US vendors are prohibitively expensive.