The Mind Guardian was the individual born to represent, serve, and protect the Pillar of the Mind, one of the Pillars of Nosgoth. All Pillar Guardians belonged to the oligarchy of sorcerers known as the Circle of Nine.
The Mind Guardians were the guardians of the Pillar of the Mind. Their abilities lay in psychological properties such as thoughts and emotions which they were apparently sensitive to in others. They also had many exotic mental abilities such as Telepathy Telekinesis and the ability to create illusions.
Three mind guardians have been observed in the series, of these Nupraptor the Mentalist is the only one who is named, and it is he whose mental prowess and psychic powers ultimately lead to the Corruption of the Pillars, through an attempted psychic attack on Mortanius (though this may also be characterised as a "descent into madness") which effects all of the circle, the pillars and eventually Nosgoth itself.
Two of his predecessors have also been seen. The original Vampire Mind Guardian, whose soul was taken along with the original Vampire Dimension Guardian, to forge the Reaver with elemental Air in Legacy of Kain: Defiance (This vampire mind guardian, much like Nupraptor himself, attacked by utilising illusions).
Finally a Mind Guardian is known to have been murdered by Vorador, it is unknown if his murder was depicted during Blood Omen: Legacy of Kain, but his picture will have been in the memorial room in the Soul Reaver 2, although which figure represents this guardian is open to interpretation.