McDonalds is a chain of fast food restaurants, inside of which people eat McDonalds' fast food. Their fast food is notable for making you fat, and so its fast food is also fat food, making it… fat-st food? The brand's logo, referred to as the Golden Arches, was designed to look like a pair of shiny gold mammaries.
The McDonald's restaurant was first mentioned in a song by Japanese smooth jazz collective Alice in Chains. The song was called McDonald's Baby, and it was featured as the overworld level theme in Super Mario Bros. 3. When the Super Mario Bros. movie was released, twelve Burger King restaurants in America were converted to McDonald's in reference to the Mario 3 game. However, they proved so popular with the consumerist slime who populates America that they stayed and eventually became a worldwide food chain. This caused the Burger King to retaliate, jetisonning the world into The First Fast Food War and ruining civilization forever.
In the Super Mario series, Mario goes into a McDonalds at the end of each level after pulling down a Goal Pole. McDonalds restaurants have filled this role in Super Mario Bros. and the New Super Mario Bros. series. Though Super Mario 3D Land and Super Mario 3D World have Goal Poles, McDonalds do not appear alongside them, save for a minor appearance in some SMB1-themed levels in the former.
McDonalds also appears as a stage in the 1996 arcade fighting game Mario Fighters. A player can break in and steal food to throw at the other fighter.
A McDonalds appears in Mega Man 5 as McMan's stage.