  We study the singularity created in the supercritical collapse of a spherical
massless scalar field. We first model the geometry and the scalar field to be
homogeneous, and find a generic solution (in terms of a formal series
expansion) describing a spacelike singularity which is monotonic, scalar
polynomial and strong. We confront the predictions of this analytical model
with the pointwise behavior of fully-nonlinear and inhomogeneous numerical
simulations, and find full compliance. We also study the phenomenology of the
spatial structure of the singularity numerically. At asymptotically late
advanced time the singularity approaches the Schwarzschild singularity, in
addition to discrete points at finite advanced times, where the singularity is
Schwarzschild-like. At other points the singularity is different from
Schwarzschild due to the nonlinear scalar field.
