William Mitcheson Timlin (11 April 1892 – 7 June 1943) was an architect and illustrator. He was born in Ashington, Northumberland, the son of a colliery foreman. He showed talent for drawing at Morpeth Grammar School, and received a scholarship to the Armstrong College of Art in Newcastle. In 1912, he joined his parents in South Africa where he completed his training in art and architecture and remained for the rest of his life.
Timlin designed a number of important buildings in Kimberley including Kimberley Boys' High School while pursuing his interest in art, turning out a large number of watercolour fantasies in addition to oils, pastels, etchings and periodical illustrations. His work was regularly exhibited. He also wrote stories and composed music.
Timlin worked on The Ship that Sailed to Mars for two years. It was started as a diversion for his son in 1921. The work expanded until in its final form it had 48 pages of text and 48 colour plates showing remarkable flights of fantasy.
Timlin sent the book to publishers George Harrap, who were delighted with the illustrations and the calligraphic text, deciding to print it without typesetting. The book has since become a fantasy classic. The film rights to the book were purchased in the United States, where Timlin enjoyed great popularity. Alan Horne in The Dictionary of 20th Century British Book Illustrators describes the book as a masterpiece and "the most original and beautiful children's book of the 1920s".
Timlin illustrated many South African travel books and prepared illustrations for a book titled The Building of a Fairy City which was never published. He died in Kimberley, Northern Cape in 1943.