Danish artist Kay (pronounced “Kigh”) Nielsen was one of the great illustrators of the period from the late 19th to the early 20th centuries that is usually referred to as the “Golden Age of Illustration”.
Nielsen is often mentioned in the same sentence with two other amazing illustrators, who were at the top of an impressive list of amazing illustrators from that period, Arthur Rackham and Edmund Dulac.
Like Rackham and Dulac, Nielsen was very influenced by Alphonse Mucha and Art Nouveau, the Pre-Raphaelite painters and romantic art. The terrific Swedish illustrator John Bauer was also undoubtedly influential on all three as well.
More than the others, however, Nielsen moved into the realm where representational imagery blended with design and the division of parts of the image into patterns and decorative elements. In this he took obvious inspiration from Aubrey Beardsley and Japanese woodblock prints, which were popular in Europe in Victorian times.
Nielsen, in turn, was influential on other artists at the time, including Rackham and Dulac and later illustrators such as Dorothy Lathrop. You can also see his influence in modern illustrators and even comic book artists like P. Craig Russell.
Nielsen illustrated a number of classic books of fairy tales and is perhaps most noted for his work on East of the Sun and West of the Moon: Old Tales from The North.
Late in his career, he became interested in animation and went to work for Disney, contributing designs to Fantasia (notably the Bald Mountain sequence) and its intended follow-up. His style and working methods were not a good match for the high-paced demands of the animation business, however, and his time there was brief.
There is a collection of his work, Nielsen’s Fairy Tale Illustrations in Full Color, another of work from his estate called Unknown Paintings of Kay Nielsen (David Larkin), and you may be able to find some of the fairy tale books with his illustrations, including East of The Sun and West of the Moon: Old Tales from The North.