In the usual approach to the pilot-wave theory for a spin zero particle one starts with the Klein-Gordon equation, which is the relativistic generalization of the Schrodinger equation. This approach encounters several difficulties including superluminal motion and particle trajectories that move backwards in time.
In this paper I start with the relativistic classical Hamilton-Jacobi equation and introduce the quantum potential in a way that avoids the above mentioned difficulties. Particle trajectories are timelike or null and are future pointing. The wave equation satisfied by the field is a nonlinear generalization of the Klein-Gordon equation.