  A unification of Klein--Gordon, Dirac, Maxwell, Rarita--Schwinger and
Einstein equations exact solutions (for the massless fields cases) is
presented. The method is based on writing all of the relevant dynamical fields
in terms of products and derivatives of pre--potential functions, which satisfy
d'Alambert equation. The coupled equations satisfied by the pre--potentials are
non-linear. Remarkably, there are particular solutions of (gradient) orthogonal
pre--potentials that satisfy the usual wave equation which may be used to
construct {\it{exact non--trivial solutions to Klein--Gordon, Dirac, Maxwell,
Rarita--Schwinger and (linearized and full) Einstein equations}}, thus giving
rise to a unification of the solutions of all massless field equations for any
spin. Some solutions written in terms of orthogonal pre--potentials are
presented. Relations of this method to previously developed ones, as well as to
other subjects in physics are pointed out.
