But last year, Mars Inc. gave Hershey a run for their money when M&Ms overtook Reese’s as that year’s most popular Halloween candy. A few different factors have helped Mars and Hershey maintain their Halloween aisle hegemonies year after year. In 1937, the government approached the candy-maker and asked them to make a calorically dense chocolate bar that could withstand high temperatures. The final product, made with oat flour, cocoa butter, sugar, chocolate, skim milk powder, and vitamin B1, was dense as a brick. An entire post-war generation grew up with M&Ms, along with “The Great American Chocolate Bar,” as the Hershey’s bar was once called.