Abstract: The present invention relates to a retractable king pin assembly for a trailer operable between an extended position, for engagement with a truck or tractor fifth wheel, and a retracted position, wherein the king pin is retracted to prevent engagement by a fifth wheel to permit the trailer to be left unattended without the threat of being stolen. The king pin security device includes a base member having an aperture, a king pin disposed in the base member aperture, and an actuator operatively connected to the king pin. The actuator either rotates or slides the king pin to move it in an axial direction between the extended and retracted positions. The actuator can include an electric motor, a solenoid or a hydraulic or pneumatic cylinder.