An actuator for actuating a torque transmission device, comprising a translationally movable drive element and a slidable piston of a piston-cylinder unit for the purpose of producing a fluid volumetric flow in order to actuate the torque transmission device, wherein the drive element and the piston are fixedly connected to each other in a form-fitting manner in the axial direction merely by means of shaped elements of the piston and of the drive element themselves, for the purpose of sliding of the piston by means of the drive element, wherein the drive element is a rotationally fixedly arranged and translationally displaceable spindle of a spindle drive, in particular of a planetary rolling gear, characterised in that the shaped elements of the piston and of the drive element realising the mechanical connection are components of a bayonet catch, by means of which the piston is fixed to the drive element, in that the actuator has a reinforcing element that fixes the two sides of the bayonet catch in their circumferential positions in relation to one another in a force-fitting and/or form-fitting manner, in that the bayonet catch has at least one engagement element (31, 34) on each of the two sides, and a respective engagement element (31, 34) of one side is set up to engage in an engagement element (31, 34) of the other side of the bayonet catch or to be engaged by the engagement element (31, 34) of the other side, such that the bayonet catch has at least one pair of engagement elements (31, 34) engaging in one another, and in that the reinforcing element has a ring region, from which a plurality of webs extend in the axial direction, wherein the webs are arranged in such a way that they block a relative rotational movement of the engagement elements (31, 34) arranged in pairs in a form-fitting manner, wherein the piston has a first radial shoulder radially outwardly and a second radial shoulder axially opposite thereto and a groove formed between the two shoulders (21, 22) in which a sealing ring is mounted, and wherein the piston also receives the reinforcing element, such that a sealing lip of the sealing ring is supported in the axial direction by the reinforcing element. in that the actuator has a reinforcing element that fixes the two sides of the bayonet catch in their circumferential positions in relation to one another in a force-fitting and/or form-fitting manner, in that the bayonet catch has at least one engagement element (31, 34) on each of the two sides, and a respective engagement element (31, 34) of one side is set up to engage in an engagement element (31, 34) of the other side of the bayonet catch or to be engaged by the engagement element (31, 34) of the other side, such that the bayonet catch has at least one pair of engagement elements (31, 34) engaging in one another, and in that the reinforcing element has a ring region, from which a plurality of webs extend in the axial direction, wherein the webs are arranged in such a way that they block a relative rotational movement of the engagement elements (31, 34) arranged in pairs in a form-fitting manner, wherein the piston has a first radial shoulder radially outwardly and a second radial shoulder axially opposite thereto and a groove formed between the two shoulders (21, 22) in which a sealing ring is mounted, and wherein the piston also receives the reinforcing element, such that a sealing lip of the sealing ring is supported in the axial direction by the reinforcing element.