Kay Rasmus Nielsen (March 12, 1886 – June 21, 1957) was a Danish illustrator who was popular in the early 20th century, the Golden Age of Illustration which lasted from when Daniel Vierge and other pioneers developed printing technology to the point that drawings and paintings could be reproduced with reasonable facility.

A year later in 1914, Nielsen provided 25 colour plates and more than 21 monotone images for the children's collection East of the Sun and West of the Moon.

During this time, Nielsen also worked on an extensive suite of illustrations intended to accompany a translation of The Arabian Nights that had been undertaken by the Arabic scholar, Professor Arthur Christensen.

During that time, at age 40, he married the charismatic 22-year-old Ulla Pless-Schmidt, daughter of a wealthy physician,[3] and they became a devoted couple.

[4] Following his theatrical work in Copenhagen, Nielsen returned to contributing to illustrated books with the publication of Fairy Tales by Hans Christian Andersen in 1924.

A year later, Nielsen provided the artwork for Hansel and Gretel, and Other Stories by the Brothers Grimm which was first published with 12 colour images and over 20 detailed monotone illustrations.

[2] Kay Nielsen continues to be credited for his work at the Disney company and is ascribed for inspiring the visual development of Frozen.

[9] Before her death to diabetes, Ulla gave Nielsen's remaining illustrations to fellow artist and architect Frederick Monhoff, who in turn tried to place them in museums.