Monkey Day is an unofficial holiday observed on December 14, 2017. The day takes place annually and is celebrated internationally. It was started in 2000 by Casey Sorrow. On December 14th he jokingly scribbled Monkey Day on a friend's calendar. Lansing residents and students off Michigan State University started to celebrate Monkey Day.
The day gained notoriety when Casey Sorrow and Eric Millikin's own comic strip began promoting it along with other cartoonists. Monkey Day is celebrated in many different countries around the world, primarily with costume parties. It is intended to help draw attention to issues related to simians, including medical research and animal rights. The holiday cuts across religious boundaries and provides opportunities to share monkey stories and contemplate our simian relatives. Hallmark Cards describes it as the day, when monkey business is encouraged.
Casey Sorrow is an American cartoonist, illustrator, and printmaker. His early comic collaboration with Eric Millikin, Fetus-X, was run for a short time in Michigan State University's State News, until the comic strip was removed for being too controversial. Casey Sorrow is known as the inventor of the holiday Monkey Day, on which in some years Monkey Day Web Comic Marathons take place.