An actuator (22) comprises at least one actuator body (32) of dielectric elastomeric material and two electrodes (34, 36) being attached to opposite surfaces of the actuator body (32), respectively. At least one of the actuator body (32) and at least one of the electrodes (34, 36) is at least partly covered at its outer side with a protective layer (38a, 38b) of polymer material, wherein a mechanical stiffness of the protective layer (38a, 38b) is at least three times lower than a mechanical stiffness of the actuator body (32). Moreover, a valve actuator unit comprises such an actuator (22) and a housing, wherein the actuator (22) is arranged within the housing and the remainder of the housing is filled with a gas. Additionally, a valve comprises such a valve actuator unit and a valve element, wherein the valve element is movable by the valve actuator unit.