The Monoptrian is a clone, apparently of some extraplanar warlord who wished to both form an unstoppable army and become immortal. He (or it, more accurately; no one has properly studied Monoptrian gender) accomplished both ambitions by cloning himself in a process that could become self-perpetuating after his death.
Of course, things are rarely so simple. Flaws in the cloning process ensured that descendants would become increasingly degenerate, forming mutant variants that probably have little in common with their progenitor. Of course, the degenerate offspring have little knowledge of this fact, with several variants forming factions under some rogue leader or other.
Naturally, each faction claims to be the "pure" one, and the only one fit to overwhelm the planes in the name of their progenitor.
As such, this race of super-soldiers is less of a threat than it first appears, as it seems unlikely that they will ever organize enough to begin their conquest. Of course, there are always rumors regarding all sorts of things — that the progenitor is still alive and waiting to take control of the entire army; that a messiah will rise from the ranks of the clones; that a subtle Monoptrian faction secretly runs the Illustrious Menagerie of Peacocks; or that some power player has determined the signal that will gain control of the whole army — but those are only rumors, right?
The following Monoptrian represents an agile warrior of his clan. Individual Monoptrian specimens may vary considerably, and indeed, are only really unified by the immunity to Charm and the monoptrian keyword (additionally, they all tend to bear the same slender, monocular physique). Depending upon circumstances, other specimens may use other weapons, represent other levels or monster roles, and may have different varieties of eye-beams (enterprising DMs wanting to customize this creature may wish to give it a different weapon, although damage will be the same, and may also wish to change the eye-beam by changing status effects and damage types). In combat, this Monoptrian will typically open with Eye-Beam to daze an opponent, and then move into melee to take advantage of the confusion with Staff. It tries to use Eye-Beam whenever it recharges, either using it in melee against dazed opponents or using Combat Agility to move out of range of opportunity attacks. Monoptrians fight intelligently, but will fight to the death if necessary. Depending on the variety, they may also make decisions based on the good of the collective — one Monoptrian might draw the party's fire if it means that its fellows can better complete a mission objective.