McDonald's first nationally advertised breakfast menu item introduced in 1971 was the Egg McMuffin.
Herb Peterson, a McDonald's franchise owner in Santa Barbara, California, created the sandwich in the early 1970s. It used an English muffin, a round egg, Canadian bacon, and cheese, giving McDonald's a portable breakfast product modeled in part on eggs Benedict.
The Egg McMuffin was first tested locally before McDonald's expanded breakfast more broadly. Its success helped establish breakfast as a major daypart for the chain and provided a signature product that could be identified with McDonald's outside the traditional lunch and dinner hours.
The Egg McMuffin is sometimes confused with the later McGriddle, which launched in 2003 and uses griddle cakes. The Egg McMuffin's 1971 introduction came decades before McDonald's breakfast became an all-day marketing focus in many markets.