  The Landau gauge quark propagator in momentum space is investigated using the
O(a)-improved Sheikholeslami--Wohlert (SW) quark action with a tree-level
mean-field improved coefficient c_sw. We have studied the unimproved definition
of the quark propagator, as well as two different tree-level O(a)-improved
propagators. The ultraviolet behavior of the free lattice propagator is studied
for each of these in order to establish which of them provides the most
reliable description of the quark propagator up to the medium momentum regime.
A general method of tree-level correction is introduced. This exploits
asymptotic freedom and removes much of the trivial lattice artifacts at medium
to high momenta. We obtain results for the quark propagator which are
qualitatively similar to those typically used in quark models. A simple
extrapolation of the infrared quark mass M(p^2=0) to the chiral limit gives
(298+/-8+/-30) MeV, which is consistent with phenomenological expectations.
