Who is Ruth Black in Foer's Extremely Loud and Incredibly Close?

Ruth Black is the unofficial tour guide who lives at the
top of the Empire State Building.  Oskar meets her with Mr. Black.  She either sleeps on
the observation deck itself or in one of the storage rooms when it is cold.  Though the
situation seems immediately strange both to Mr. Black and to Oskar, she explains quite
simply that no one has ever told her to go home.

When he
was alive, her husband used to shine a spotlight from the city up to the Empire State
Building so that she could see it from above.  When he died, Ruth came back to the top
of the building and has remained ever since.  She lives (allegedly) off of food from one
of the two snack bars at the top or occasionally one of the "young men" will bring her
food.

She does not provide any clues to the mystery of the
key, and after leaving the Empire State Building that day, Oskar's companion (Mr. Black)
announces he's finished with the search.