The Egg McMuffin was McDonald's first major breakfast sandwich, introduced nationally in 1975.
Herb Peterson, a McDonald's franchise owner in Santa Barbara, California, created the sandwich in the early 1970s. He used an English muffin, a round egg, Canadian bacon, and cheese to make a portable breakfast item that resembled an eggs Benedict-style meal.
McDonald's tested the sandwich before expanding it nationwide in 1975. Its success helped establish breakfast as a major part of the McDonald's brand rather than a limited morning offering. The product also showed how the company could turn a franchise invention into a standardized national identity.
The Egg McMuffin is sometimes confused with the Sausage McMuffin, which is a related menu item but not the original sandwich. The McGriddle arrived much later, in 2003, and belongs to a different generation of breakfast branding.