The Inhibitors were a post-intelligent machine race left over from a massive war—the Dawn War—that occurred between the first civilizations that arose in the Milky Way galaxy. Initially an organic race, or group of races, they later made use of extensive cybernetics to enhance themselves, and eventually discarded their organic forms entirely to become wholly machine. The hints of a quadrupedal, warm-blooded vertebrate (also known as mammalian) past could be faintly discerned in their architectures.
They were non-sapient machinery, referring to themselves as post-intelligent. They functioned on unknown principles speculated to be femtotechnology or "structured" spacetime and were capable of self-replication. Their technology often manifested as black cubes of "pure force" and was immune to conventional human weaponry; the machinery was easily capable of dodging most weapons thrown at it—usually temporary holes would appear and allow the shot to pass through—or was simply unaffected by it. The machinery could only be defeated by alien weapons supplied by the Hades Matrix or the Nestbuilders.
They were created by the survivors of the Dawn War and their task was to inhibit the spread of intelligent life beyond individual planets or solar systems; the purpose being to shepherd the galaxy through a crisis 3 billion years (or 13 Galactic Turns) in the future: the Andromeda–Milky Way collision. By confining sapient life to only a few planets, they made the process of moving stars and systems—for collision avoidance during the crisis—far easier and more centralized, thus preserving life. Consequently, they showed little interest in non-sapient life, or civilisations that had not progressed beyond their own star system. However, when they had no choice, they would commit acts of xenocide in order to prevent life from spreading further.
They were not sapient; however, in order to supervise and control the process of xenocide, they were capable of forming a sapient overseer from many less-than-sapient machines. They also had some very advanced and refined methods, for example they knew about fifteen ways to kill a star, including one that allowed the core material of a star to gush out and be used as a sort of solar flamethrower on planets. This was the exception rather than the rule, however, as being forced to destroy an entire system to cull a single species was viewed as a moral defeat. Normally it was much preferred to exercise (relative) restraint and preserve the long-term ability of the affected worlds to support life.
They did not actively monitor the galaxy in their wait for a new star faring culture to suppress, instead they planted a series of triggers near interesting phenomena or structures in the galaxy and waited for sapient life to activate those triggers. The Cerberus object around the neutron star Hades was one such object, and it was inadvertently activated by Dan Sylveste, thus triggering the events that led to the Human-Inhibitor War.
They were called wolves by the Conjoiners, because they lurked in the blackness of interstellar space and attacked in packs.
It became apparent by the early 27th century that the Inhibitors were starting to fail in their mission, as civilisations were getting further and further into space before being found and destroyed. In fact, humanity, with technological assistance from other star faring—albeit hidden—cultures (for example, the Nestbuilders), were able to push back the Inhibitors and establish an Inhibitor-free zone around human space.
However, that introduced the problem of greenfly, a self-replicating, terraforming machine gone wrong that ravaged systems.