  In this Chapter we present the motivation for undertaking both a wide and
deep survey with the SKA in the context of studying AGN activity across cosmic
time. With an rms down to 1 $\mu$Jy/beam at 1 GHz over 1,000 - 5,000 deg$^2$ in
1 year (wide tier band 1/2) and an rms down to 200 nJy/beam over 10 - 30
deg$^2$ in 2000 hours (deep tier band 1/2), these surveys will directly detect
faint radio-loud and radio-quiet AGN (down to a 1 GHz radio luminosity of about
$2\times10^{23}$ W/Hz at $z=6$). For the first time, this will enable us to
conduct detailed studies of the cosmic evolution of radio AGN activity to the
cosmic dawn ($z\gtrsim6$), covering all environmental densities.
