Theory Z is a name for various theories of human motivation built on Douglas McGregor's Theory X and Theory Y. Theories X, Y and various versions of Z have been used in human resource management, organizational behavior, organizational communication and organizational development.
McGregor's Theory X states that workers inherently dislike and avoid work and must be driven to it, in contrast to Theory Y which states that work is natural and can be a source of satisfaction when aimed at higher order human psychological needs.
One Theory Z was developed by Abraham Maslow in his paper Theory Z which was published in 1969 in the Journal of Transpersonal Psychology.
The second one is the 3D Theory which was developed by W. J. Reddin in his book "Managerial Effectiveness" (1970).
And the other is William G Ouchi's so-called "Japanese Management" style which was explained in his book "Theory Z: How American Business Can Meet the Japanese Challenge" (1981); such style was popularized during the Asian economic boom of the 1980s.
For Ouchi, Theory Z focused on increasing employee loyalty to the company by providing a job for life with a strong focus on the well-being of the employee, both on and off the job. According to Ouchi, Theory Z management tends to promote stable employment, high productivity, and high employee morale and satisfaction.