Mark Ellery Haas (1952 – 18 February 2007) was a modern-day Oz author and illustrator. His publications are The Medicine Man of Oz (2000) and Leprechauns of Oz (2001).
When publishing his first book, Haas asked permission from the L. Frank Baum Family Trust. Instead of approval he received legal threats: he was told that he had violated the copyright of The Giant Horse of Oz, in which his title character, Herby the Medicine Man, first appeared.
Haas's third Oz book, The Emerald Mountain of Oz, was published posthumously and is available through the website www.dennisanfuso.com.