  We provide constraints on the nature of the optically faint (I>=24) X-ray
source population from a 1 Ms Chandra exposure of a 8.4x8.4 arcmin region
containing the Hubble Deep Field North. We detect 47 (2,400 deg^-2) optically
faint X-ray sources. The fraction of optically faint X-ray sources is
approximately constant (at approx 35%) for 0.5-8.0 keV fluxes from 3x10^-14 cgs
down to the X-ray flux limit. A considerable fraction (approx 30%) of the
sources are Very Red Objects (I-K>=4). Analysis of the optical and X-ray
properties suggests a large number of optically faint X-ray sources are likely
to host obscured AGN activity at z= 1-3. From these results we calculate that a
significant fraction (approx 5-45%) could be obscured QSOs at z<=3. Given the
number of X-ray sources without I-band counterparts, there are unlikely to be
more than approx 15 sources at z>6. We provide evidence that the true number of
z>6 sources is considerably lower. Nine optically faint X-ray sources have
micro-Jy radio counterparts; approx 53% of the optically faint micro-Jy radio
sources in this region. The most likely origin of the X-ray emission in these
X-ray detected, optically faint micro-Jy radio sources is obscured AGN
activity. However, two of these sources have been previously detected at
sub-millimeter wavelengths and the X-ray emission from these sources could be
due to luminous star formation activity. Assuming the SED of NGC 6240, we
estimate the 175 micron flux of a typical optically faint X-ray source to be
<10 mJy. As expected for sources with AGN activity, the two optically faint
X-ray sources within the most sensitive area of the ISOCAM region have faint
(approx 50 micro-Jy) 15 micron counterparts. (ABRIDGED).
