Everybody knows and loves M&M’s, but few know how they came to be.

During the Spanish Civil War, Forrest Mars Sr. saw soldiers eating chocolate pellets surrounded by a hard shell that was designed to prevent them from melting. Mars took this clever idea and patented his own version in 1941 and, in the process, created one of the best-selling candies in history.

During World War II, M&Ms were sold exclusively to the military. In 1954, the slogan that Elizabeth Granberry Hill McKean wrote was trademarked, harkening to the candy’s original purpose: The milk chocolate that melts in your mouth, not in your hand.