Etymology
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Kilroy 
U.S. military graffito character, 1945, said to be either Sgt. Francis J. Kilroy Jr., U.S. Army Air Transport, whose friend or friends began writing his name everywhere as a prank; or war materiéls inspector James J. Kilroy of Quincy, Mass., who wrote "Kilroy was here" on everything he checked.
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chad (n.1)

also Mr. Chad, simple graffiti drawing of a head peering over a fence or wall, with the caption, "Wot, no ______?" (the U.S. version usually had "Kilroy was here"), 1945, British, of unknown origin, a reaction to war-time shortages and rationing.

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