Omnius, also known as the Evermind, was a collection of powerful artificially intelligent entities, which existed prior to and during the Butlerian Jihad, and after in the refounded Synchronized Worlds outside the Old Empire.
Though Omnius instances existed on many worlds, each one evolving subtle differences, all instances were bound by a synchronizing process that saw them share the collective experiences of their counterparts. Thus they were frequently referred to as a single being.
Omnius is often cited as the cause of the mankind's long-standing revulsion of technology, particularly computers. Though technically a gender-less being, historical accounts most often refer to Omnius as a male.
Inception
Accounts cite Omnius as coming into existence during the Time of Titans when the Titan Xerxes ceded too much control to the AI gel circuitry network on one of his planets.
The AIs were already programmed by Barbarossa to have ambition and expansion tendencies, in order to facilitate the Titans' rebellion. Omnius therefore, as the intelligence christened itself, quickly took control of the Titan-ruled worlds and brought his own clinical and logical rule to them. Barbarossa however had secured some algorithms that prevented these programs/Omnius to harm the Titans themselves; although Omnius took control of the Titans, it didn't show any will to get rid of them.
History and incarnations
The vast size of the Omnius-controlled empire proved to be problematic when disseminating and synchronizing information. Thus the Evermind deployed planet-wide clones of himself across his empire, each of which acted technically as equals. However, in practise one incarnation took the initiative with empire wide decisions. This incarnation, known as Omnius Prime, was first located on Earth.
Knowledge was distributed between the various Omnius incarnations via Update Ships, which delivered gel circuitry copies of an Evermind from one planet to another via faster-than-light travel. This cumbersome method was accepted by Omnius because no better solution was discovered or made available. The discovery of faster-than-light space travel by the League of Nobles was a jealously guarded (and successfully kept) secret.
Erasmus had put a sort of experimental bet with Omnius Prime concerning the predictability of humans: Erasmus proposed Omnius to randomly select some loyal trustees, and himself would demonstrate that he could turn them against the thinking machines; this would prove whether reliable humans could be trusted. Omnius however warned Erasmus that if the humans indeed proved unworthy, he would vehemently order their extinction, to Erasmus' dismay, since he would have no experiments.
The wage however turned against Omnius and a rebellion on Earth started, which started the Butlerian Jihad. Omnius' retaliation was the extermination of all human slave population on Earth and sent the Dream Voyager with an update copy of himself to warn the Synchronized Worlds about the event and proceed with the extinction order. However Earth-Omnius himself was destroyed during the assault of the League Worlds, and the update copy of Omnius was captured by Vorian Atreides. After that event, the Omnius of Corrin became the Omnius-Prime, who was ignorant of the details of the abortive wager. The only robotic living witness of the details of was Erasmus, who however kept it to himself.
Defeat
By the end of the Butlerian Jihad, and specifically after Omnius had unleashed the Omnius Scourge virus upon the League of Nobles, his empire had been reduced to a single planet - Corrin. The virus' catastrophic effect on the free humans drew a fierce counter-strike campaign of nuclear obliteration against the Synchronized Worlds. This event, known more commonly as the Great Purge, ultimately left Omnius pinned down on Corrin for many years.
The last incarnation of Omnius was finally defeated by the armies of free humanity at the Battle of Corrin.
Unbeknownst to the free humans, their victory was not entirely complete. Years before, before the start of the Jihad, an Omnius incarnation on Giedi Prime had attempted to expand into uncharted space as a means of preserving its legacy. To that end the Giedi Prime Omnius distributed large quantities of probes carrying Omnius gelspheres. The probes contained sufficient automization and a self-powered gelsphere, and upon arriving on other worlds were able to synthesize and produce new robotic servants and a new incarnation of the robotic empire. The actions of this Omnius incarnation were never learned by the other Omnius instances, and not fully realized by humanity.
Additionally, in the final Corrin battle the Omnius transmitted radio signals into deep-space containing the whole of his psyche. The scheme was a last, desperate grasp at life by the final Omnius instance. It was unlikely to succeed because the signals were unlikely to reach anything capable of intercepting them before they had dissipated beyond use. Unfortunately for the humans, this transmission reached the hidden robotic empire, and their long-time enemy was effectively reborn.
Legacy
The oppression of humans by artificial intelligences remained a powerful concept for tens of thousands of years. The physical and psychological damage caused by Omnius succeeded in scarring the human psyche far deeper than any other historical event.
Personality
Though Omnius theoretically possessed no feelings and thus no tangible personality, accounts exist that dispute this. In particular, subtle differences in the reactions of the Omnius incarnations on Earth and Corrin were noted; with the Earth-Omnius exhibiting tolerance toward the experiments and theories of the robot Erasmus, whereas the Corrin-Omnius showed a distinct lack of patience with the rogue robot. Additionally, the Corrin-Omnius often displayed erratic, even paranoid, behaviour. This tendency was exacerbated after he incorporated a copy of Erasmus into his psyche.
Behind the Scenes
Omnius features heavily in the Legends of Dune trilogy written by Brian Herbert and Kevin J. Anderson. The various Omnius incarnations constitute the Synchronized Worlds, which jockey with the League of Nobles for control of the Known Universe. Omnius is not mentioned in the original Dune novels by Frank Herbert.
The name Omnius is obviously derived form the Latin root omni-, referring to his simulated omnipresence and omniscience. Like the word 'evermind', it refers to his nature of having copies of himself in all of his subjects.