Kilroy Was Here represents one of the earliest examples of viral imagery and messaging, predating the internet by decades. The image, a simple bald man peeking over a wall with his large nose prominent, combined with the caption 'Kilroy Was Here' became instantly recognizable. The meme represented military camaraderie and the desire to mark presence in unexpected places. The simplicity of the drawing and the catchiness of the phrase made both highly replicable. When the image was discovered by web culture, it was immediately recognized as a historical meme, representing an analog precursor to digital memetic culture. The meme's meaning, establishment of presence in a space, translated naturally to online contexts.

The exact origins of Kilroy remain somewhat mysterious, with multiple origin stories. The most widely accepted account traces Kilroy to American military culture during WWII, where soldiers created the image and phrase as a form of marking their presence. The image appeared on military equipment, in barracks, and in unexpected locations worldwide as soldiers spread it during the war. Post-war, the image continued to appear as graffiti. When meme culture emerged in the 1990s, early adopters recognized Kilroy as a historical example of viral messaging. The image appeared in early forums and messageboards as users familiar with the historical meme incorporated it into online culture.

Kilroy memes were primarily used by drawing or writing 'Kilroy Was Here' in unexpected locations to mark presence. In online contexts, the image was posted to establish that one had been in a particular space or thread. The meme functioned similarly to signatures in early online forums.