  We present an exploration of the expected detection of the earliest Active
Galactic Nuclei (AGN) in the Universe from state-of-art galaxy formation and
evolution semi-analytic models and hydro-dynamical simulations. We estimate the
number and radiative characteristics of Super Massive Black Holes (SMBHs) at
$z\geq 6$, a redshift range that will be intensively explored by the next
generation of telescopes, in particular in the radio through the Square
Kilometre Array (SKA) and at high energies with ESA's Athena X-ray Observatory.
We find that Athena will be able to observe over 5000 AGN/$\rm deg^2$ at the
Epoch of Re-ionization (EoR), $6\leq z \leq 10$. Similarly, for the same
redshift range the models/simulations suggest that SKA will detect at least 400
AGN/$\rm deg^2$. Additionally, we stress the importance of the volume of the
simulation box as well as the initial physical conditions of the
models/simulations on their effect on the luminosity functions (LFs) and the
creation of the most massive SMBHs that we currently observe at the EoR.
Furthermore, following the evolution of the accretion mode of the SMBHs in each
model/simulation, we show that, while the quasar dominates over the radio mode
at the EoR, detection at radio wavelengths still reaches significant numbers
even at the highest redshifts. Finally, we present the effect that the
radiative efficiency has on the LFs by comparing results produced with a
constant value for the radiative efficiency and more complex calculations based
on the spin of each SMBH.
