WWII, Art, History
Some say "Kilroy was here" is one of the earliest examples of what is today called a "meme". An inside joke of sorts that isn't linked to a specific person and that pops up all over the place. "Kilroy was here" was popular with allied servicemen in World War II. Seeing Kilroy is a reminder that you're not alone. Somebody was here before you. Somebody was also a person, with thoughts and feelings, who shared a bit of their presence with you in the form of Kilroy. There is some debate as to where Kilroy originated. He's gone by quite a few different names over the years and around the world, likely originating in Australia as "Foo was here".