Cliff Nielsen

Cliff Nielsen is best known for designing the covers for The Mortal Instruments series and The Infernal Devices trilogy by Cassandra Clare.

Above are eight of Nielsen's covers for Cassandra Clare's novels The Mortal Instruments and The Infernal Devices. I am pretty certain that Nielsen will design the covers for The Dark Artifices, The Last Hours and The Wicked Powers also by Cassandra Clare. 

John Rocco

John Rocco is an American illustrator and author from Brooklyn, NewYork City. Rocco is best known for illustrating the covers for The Percy Jackson series, The Kane Chronicles and The Heroes of Olympus series by fellow author Rick Riordan.

Above is the cover for The Heroes of Olympus: the House of Hades which was designed by Rocco. His drawing style is very similar to that of Arthur Rackham's but with a lot more colour but they still deliver the same nightmarish effect. 

Arthur Rackham

Arthur Rackham was a children's book illustrator who was born in the 1860s. Rackham is apart of what is now known as the Golden age of illustration. He has illustrated the likes of Peter Pan in Kensington Gardens by J.M. Barrie and Shakespeare's A Midsummer's Nights Dream.

Above is one of Rackham's illustrations for Alice in Wonderland by Lewis Carroll. Rackham's illustrations are very dark and nightmarish and they are very memorable as one can never forget nightmares. Rackham used pen and ink to draw his illustrations as Computers were only invented in the decade that he died.