Connector for connecting at least one fluid line to another fluid line or to an assembly connection, comprising a housing with a through channel, one end of the housing being designed as a sleeve section for inserting a mating connector, and having latching means (10, 12) for releasably fixing the mating connector, the latching means (10, 12) being a component of an adapter sleeve which can be plugged into the sleeve section and is held in the sleeve section by means of radially elastic positive locking elements and has a through-opening for a plug shank of the mating connector, and the latching means (10, 12) are formed from at least two first latching arms which are radially elastic in relation to a longitudinal center axis (X-X) of the connector and the first latching arms have at their free ends first latching cams extending radially in the direction of the longitudinal center axis (X-X), wherein the positive locking elements are formed from radially elastically bendable arms formed on the outer circumference of the adapter sleeve between the first latching arms and each extend parallel to the longitudinal center axis (X-X), which lie diametrically opposite one another and have second latching cams at their free ends pointing in the insertion direction, which project outwards, wherein the positive locking elements, in their inserted state into the sleeve section, engage in a positively locking manner with the second locking cams in locking recesses in the circumferential wall of the sleeve section, and a release lock is arranged on the outer circumference of the sleeve section so as to be displaceable in the direction of the longitudinal center axis (X-X) between two latching positions, wherein the release lock in its second latching position displaced on an annular collar of the adapter sleeve prevents spreading of the latching arms and in its other first latching position the latching arms can be spread, and the release lock consists of a sleeve which surrounds the sleeve section, which has, on its circumferential edge pointing in the insertion direction, first latching tongues which, in the respective latching position, latch into first and second recesses (65, 30) in the circumferential wall of the sleeve section in a force-locking manner, characterized in that the sleeve of the release lock has hook-shaped latching extensions on its edge pointing in the direction opposite to the insertion direction, which, in the first latching position of the release lock, engage in the respective latching recesses and are fixed in a form-fitting manner counter to the insertion direction, and the second latching cams of the positive locking elements in such a way have an actuating projection pointing in the direction of the longitudinal axis (X-X), in that, as a result of the mating connector being inserted into the adapter sleeve, the second latching cams can be displaced by a displacement dimension (d) within the respective latching recess in such a way that the second latching cams lie with their free ends in the opening plane of an outside opening of the respective latching recess, as a result of which the hook-shaped latching extension is released from its positively locking latching position.