Trustees was a term used in the Synchronized Worlds to refer to a special privileged caste of humans, above the rank of slaves. Trustees were servants of higher rank, overseeing the slaves or having some special tasks on the machines' behalf. Crew bosses wore black tunic and a headband.
Considered traitors by other humans, trustees were sometimes either egotistical individuals or simply misinformed and brain-washed humans. Trustees could ascend in ranks and some were judged adequate enough to be transformed into cymeks.
The trustees and their trustfulness was the object of a wager between Erasmus and Omnius. Erasmus proposed Omnius to randomly select some loyal trustees, and himself would demonstrate that he could turn them against the thinking machines. Omnius however warned Erasmus that if he was proven right and the humans indeed proved untrustful, he would vehemently order their extinction, to Erasmus' dismay, since he would have no experiments.
During the war, Omnius sent trustees to act as spies in the League Worlds, although cautiously, so that 'exposure' to free humanity would not turn the spies against Omnius. Humans that allied with the machines were often lured with offers of immortality, by as becoming neo-cymeks or receiving a life extension treatment. The existence of spies haunted the League. The concept was a quick and easy accusation used by the Jipol against the political enemies of Iblis Ginjo or Protestants against the Jihad.