Forrest Mars introduced M&M’s in 1941 with a hard sugar shell.
The candy was developed after Forrest Mars saw soldiers eating chocolate pellets with a coating that stopped them melting easily in warm conditions. He partnered with William Murrie, whose father was president of Hershey’s, and the two companies produced the new candy.
The original M&M’s were filled with milk chocolate and marked with a small letter m. Their early slogan, “Melts in your mouth, not in your hand,” highlighted the practical coating. The product was especially useful for military rations during World War II.
M&M’s originally came in a limited color range and later expanded into many varieties, including peanut, peanut butter, and crispy versions. They are sometimes confused with Smarties, another sugar-coated chocolate confection, but Smarties have a separate British and Canadian history. The 1941 launch identifies M&M’s as the candy in this question.