"Kilroy Was Here" refers to a World War II-era graffiti marking and meme consisting of a doodle of a bald man peering over a wall with the phrase. It gained popularity among American servicemen, who used it to symbolically mark their presence in inaccessible locations across Europe and the Pacific, serving as a morale booster. Despite various theories, the true origins of 'Kilroy' remain unknown. The doodle has since evolved into a symbol of the ubiquitous presence and resilience of American forces.