Fantastic Art is an art genre. The parameters of fantastic art have been fairly rigorously defined in the scholarship on the subject ever since the time of Jules Verne and HG Wells. There was a movement of sci-fi/fantasy artists prior to and during the Great Depression, which were mainly cover art and comic book illustrators. The best anthology about them all is "Infinite Worlds: The Fantastic Visions of Science Fiction Art" by Vincent Di Fate (himself a prolific SF/space artist), with foreword by Ray Bradbury.
Fantastic Art has traditionally been largely confined to painting and illustration, but since the 1970s has increasingly been found also in photography. Fantastic art explores fantasy, space fantasy (a sub-genre of sci-fi that incorporates subjects of alien mythology and/or alien religion), imagination, the dream state, the grotesque, visions and the uncanny , as well as the so-called Goth art. Being an inheritant genre of Victorian Symbolism, the modern Fantastic Art often shares its choice of themes such as mythology, occultism and mysticism, or lore and folklore, and generally seeks to depict the inner life (nature of soul and spirit).
Fantasy has been an integral part of art since its beginnings, but has been particularly important in mannerism, magic realist painting, romantic art, symbolism, surrealism and lowbrow. In French, the genre is called le fantastique, in English it is sometimes referred to as visionary art, grotesque art or mannerist art. It has had a deep and circular interaction with fantasy literature.
The first "fantastic" artist is generally said to be Hieronymus Bosch. Other painters who have been labeled fantastic include Brueghel, Giuseppe Arcimboldo, Matthias Grünewald, Hans Baldung Grien, Francisco de Goya, Gustave Moreau, Max Magnus Norman, Henry Fuseli, Odilon Redon, Max Klinger, Arnold Böcklin, William Blake, Gustave Doré, Giovanni Battista Piranesi, Salvador Dalí, Arik Brauer, Johfra, Odd Nerdrum, and Mati Klarwein.
In the United States in the 1930s, a group of Wisconsin artists inspired by the Surrealist movement of Europe created their own brand of fantastic art. They included Madison, Wisconsin-based artists Marshall Glasier, Dudley Huppler and John Wilde; Karl Priebe of Milwaukee and Gertrude Abercrombie of Chicago. Their art combined macabre humor, mystery and irony  that was in direct and pointed contradiction to the American Regionalism then in vogue.
In postwar Chicago the major art movement, Chicago Imagism, produced many fantastic and grotesque paintings, which were little noted because they did not conform to New York abstract art fashions of the time. Major imagists include Roger Brown, Gladys Nilsson, Jim Nutt, Ed Paschke, and Karl Wirsum.