ETAOIN SHRDLU

Who or what is ETAOIN SHRDLU?

Answer:

ETAOIN SHRDLU represents the twelve most frequently used letters in written English, in order, beginning with the most used (E).  

The nonsense phrase came about in the days of "hot type" newspaper printing - where type was set using individual, hot metal molds. The letters were set aside to speed up the operation of the machine, and in case a mistake was made. The letters often accidentally appeared in print in the newspaper - often enough to become part of newspaper lore. A documentary about the final edition of the New York Times composed using hot metal (July 2, 1978) was titled Farewell, Etaoin Shrdlu.