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. Nielsen is also known for his collaborations with Disney for whom he contributed many story sketches and illustrations, not least for Fantasia.