A wave energy converter has a primary body interconnected to a secondary body such that the bodies may oscillate longitudinally relative to one another. A slug mass is visco-elastically connected to the primary body. The slug mass has effective mass, stiffness and damping characteristics. A generator is drivingly connected between the primary and secondary bodies. The generator has a load damping characteristic. At least one of the characteristics is dynamically controllable, allowing the bodies' longitudinal motion to be varied in response to wave motion changes of the wave environment in which the wave energy converter is deployed, to maintain out-of-phase oscillation of the bodies, thus increasing the driving force imparted to the generator and thereby increasing the generator's electrical energy output.