“the intelligence left over from a massive war — the Dawn War — that occurred between the first few civilizations that arose in the Milky Way galaxy. Initially an organic race, 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 can be faintly discerned in their architectures.
They are non-sapient machinery, referring to themselves as post-intelligent. They function on unknown principles speculated in the novel to be femtotechnology or “structured” spacetime and are capable of self-replication. Their technology often manifests as black cubes of “pure force” and is immune to conventional human weaponry; the machinery is easily capable of dodging most weapons thrown at it (usually temporary holes will appear and allow the shot to pass through) or is simply unaffected by it. The machinery can 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 is to inhibit the spread of intelligent life beyond individual planets or solar systems: the purpose, stated in Redemption Ark, 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 make the process of moving stars and systems (for collision avoidance during the crisis) far easier and more centralized, thus preserving life. Consequently, they show little interest in non-sapient life, or civilisations that have not progressed beyond their own star system. However, when they have no choice, they will commit acts of xenocide in order to prevent life from spreading further.
They are not sapient; however, in order to supervise and control the process of xenocide, they are capable of forming a sapient overseer from many less-than-sapient machines. They also have some very advanced technology, and know about fifteen ways to kill a star, including one that allows the core material of a star to gush out and be used as a sort of solar flamethrower on planets (shown in Redemption Ark). This is the exception rather than the rule however, as being forced to destroy an entire system to cull a single species is viewed as a moral defeat. Normally it is much preferred to exercise (relative) restraint and preserve the long-term ability of the affected worlds to support life.
They do not actively monitor the galaxy in their wait for a new star faring culture to suppress, instead they plant a series of triggers near interesting phenomena or structures in the galaxy and wait 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 at the end of the book Revelation Space, thus triggering the events in the rest of the series.
They are called wolves by the Conjoiners, because they lurk in the blackness of interstellar space and attack in packs.
In the novels it becomes apparent that the Inhibitors are starting to fail in their mission as civilisations are getting further and further into space before being found and destroyed. In fact, in the last book Absolution Gap, in the epilogue, it is shown that 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, this introduced the problem of Greenfly, a terraforming-replicator gone wrong that ravaged systems.”

http://en.wikipedia.org/wiki/Races_in_Revelation_Space#Inhibitors_.2F_Wolves

Hell, there’s no maybe about it.