Russian painter Wassily Kandinsky has always been one of my favorite artists.  He is one of the first purely abstract painters, and he is associated with the Expressionist movement in art.  He is known for the bold colors that appear in his painting, colors that he connected not only with sounds (a form of synesthesia) but also that he saw as having a spiritual dimension.

Here is one of his best-known works:

Wassily Kandinsky, Composition VII, 1913

While I think you can make a case for seeing the fantastic in this painting just as it is, there are also several works of Kandinksy's that more directly engage with fantasy and the supernatural:

Wassily Kandinsky, St. George and the Dragon, c. 1915

And there's this one, too:

Wassily Kandinsky, St. George I

The bold colors and abstract shapes of these paintings evoke a sense of other-worldliness; these are not paintings that merely portray mundane reality.  In this regard, it would seem that Kandinsky is an artist who has matched form and content--the supernatural aspect of St. George killing a dragon is reinforced by the feeling that the colors and shapes seen in the painting simply do not exist on their own in the world as we know it.