In a struggle to the death between two entities, the master emerges because they fear death less than the other, who becomes the slave. The master realizes that life without freedom is not worth living. The master's supremacy, however, is dependent on the slave's recognition. As the slave becomes self-aware, the master becomes more dependent on the slave's labor. This ultimately leads to a reversal of the hierarchy, or the slave "enslaving" the master.
Hegel’s master-slave dialectic described the perpetual struggle between the body controlling (master) and the body controlled (slave), which leads to the overthrow of the master.
Hegel,The Phenomenology of Spirit. (1807). Ebook (University of Idaho: Harper Torchbooks). http://www.marxists.org/reference/archive/hegel/phindex.htm