Kilroy is a familiar image, whose origin is something of a mystery. In 1946, the American Transit Association had a radio program called Speak to America. This program sponsored a nationwide contest in an attempt to solve the mystery behind the origins of the mystical Kilroy. Speak to America found James J Kilroy of Massachusetts as a result of their search. That James J Kilroy was the originator of 'Kilroy was here' is currently the most commonly believed explanation for the phenomenon.

James J Kilroy was a ship inspector at the Fore River Shipyard in Quincy, Massachusetts, USA. It was his responsibility to check on how many holes a riveter had filled in a shift on any given day. In order to prevent double counting by dishonest riveters and to prove to his supervisors that he'd been doing his work, he began marking 'Kilroy was here' inside the hulls of the ships being built. He used yellow crayon so it would be easily visible; this way the off-shift inspectors wouldn't count the rivets more than once and pay the riveter for work he hadn't done.

Once the ship became operative, carrying military troops that were headed overseas and bound for the war, the phrase was a complete mystery. Why it was there and being found in such out of the way places made it all the more mysterious. All they could be certain of was that Kilroy, whoever he was, had 'been there first'. As a joke, troops began placing the graffiti wherever the US forces landed and claimed it had already been there when they'd arrived.

Whoever originated it, Kilroy quickly became the United States super GI who had always already been wherever men were sent by the military. The game quickly became a challenge to put the picture and slogan in the most unlikely places imaginable first.