4e's Graduate Resident Tutor.
Aaron is actually a congealed mass of sludge that formulated in the East River of New York City. He can assume human form at convenient times.
As mentioned elsewhere, Aaron is given a wad of cash to spend on the residents of 4E. Officially this is known as the GRT budget which is made public so that the embezzlement is much less obvious.
If you would like to read the mindless drivel that encouraged the residents of 4E to interview Aaron, you can read Aarons GRT Essay