Tony DiTerlizzi is an illustrator and author who is probably best known as the co-creator of The Spiderwick Chronicles. In addition he has been the illustrator and at times author of a number of other children’s books.
The books are heavily illustrated, with interior illustrations that revive the look of the duotone process popular in the mid 20th century.
DiTerlizzi has developed a wonderfully subtle approach for his two color illustrations; his series for the first book is done in grays and muted ochres (images above, bottom two) and the second in grays and soft blues.
The illustrations for both series are beautifully realized and wonderfully imaginative, in keeping with the accolades the novels themselves have received.
DiTerlizzi has a gallery of images from A Hero for WondLa on his website. In addition, you can see a few images from The Search for WondLa in his Books gallery and sketches for the series in his Sketchbook gallery.
There is a good interview with DiTerlizzi conducted by Jonathan Liu on Wired’s GeekDad.