First identified during the transition from the Age of Uncertainty to the Era of Error, the Mysterious Footnote* has long been the subject of divellent disquisition among Philologists, Etymologists, Semanticians and other horse-thieves. While the exact date of the Footnote's primordial utilization has yet to be firmly established, experts agree that initial references to it first began to appear during the infamous work-to-rule of the Typesetter's Guild in the Century of Confusion.
Subsequent sightings -- mostly unverifiable due to the Publishers' Prohibition of the early decades of the Dates of Darkness -- are believed to have been registered in the Indices of Indeterminacy produced by licensed nitpickers during the reign of Decimus Dysphemist the Tenth. Although the indices did prompt a revival of interest in the Footnote among doctiloquents in the Academy of Addenda, paleographic speculation was palilalic and pachyglossal.
Established by Decimus as part of his campaign to limit the power of the dittographers, the Academy helped sharpen the focus on the search for the origins of the Footnote. Under the leadership of Oswaldus Ontosophistus, expert peotillomaniacs at the Academy helped relieve some of the rising pressure in the organs of state**.
* This one is reasonably clear about its own lack of mysteriousness, and therefore isn't it.
** At this point I ran out of stupidities and decided to quit while I was behind. And no, this isn't it either!