The Cyclan is a widespread organization dedicated to bringing order to the galaxy by means of pure logic. Their primary agents, Cybers, are trained from childhood in countless mental disciplines involving mathematics and reasoning, and are modified at puberty to be unable to experience any emotion. Each Cyber also possesses a biotech implant called “Homochon Elements”. These implants enable each Cyber to enter a trance-like state which enables instantaneous communication with the Cyclan central intelligence, even over interstellar distances. This central intelligence is a gestalt organism consisting of the disembodied minds of former Cybers whose mental prowess has been demonstrated to be of value but whose bodies have grown too old to continue functioning. The ultimate reward to which all Cybers aspire is to be incorporated into the central intelligence.
For these reasons, Cybers have an uncanny ability to extrapolate future events from existing data, and are highly prized (and highly paid) as advisors to rulers across the galaxy. The Cyclan publicly insists that they do not command or interfere, they merely advise, and this also increases their credibility among those who seek their service. However, the Cyclan pursue their own agenda in all things, and while they must provide valuable service to maintain their reputation, those whom they advise are always manipulated even as they are aided. While incapable of malice, the Cyclan is thoroughly ruthless and willing to sacrifice individuals or even whole worlds to their logically derived vision of the greater good. It is totally irrelevant to them whether or not the mass of humanity still handicapped by emotion shares this vision.
It is implied throughout the series that the Cyclan has something to do with all knowledge of Earth having been lost or destroyed in the distant past, and that they still strive to keep that knowledge secret. This hidden agenda puts them at odds with Dumarest from the outset of the series.
For a chronological listing of Dumarest's interaction with the Cyclan and other pertinent details about them from the novels, click here (contains spoilers).