McDonald's introduced the McDonaldland characters as a group in 1971.
McDonaldland was a fictional setting created for McDonald's advertising, with Ronald McDonald at its center and characters such as Mayor McCheese, the Hamburglar, and Grimace appearing within the same imaginative world. The setting gave the company a connected cast rather than isolated mascots.
The campaign helped McDonald's speak to children through television commercials, toys, packaging, and restaurant promotions. Its bright characters and invented locations made the brand easier to recognize and gave children recurring stories to follow.
Ronald McDonald predates the full McDonaldland ensemble, which is why 1963 is sometimes incorrectly given as the answer. That year relates to Ronald's advertising debut; 1971 marks the emergence of the broader McDonaldland character world.