The most terrifying villains of lore and ballad are archmages, liches, keenly intelligent monsters, and other beings possessing powerful magic, exceptional personal abilities, or freedom from the needs shared by many.
Aside from these, the most dangerous (and far more often overlooked) villains actually encountered in the Realms are persons of some wealth and keen intellect, who don't have the desperate financial need to do risky small robberies or constantly steal or swindle, but rather can afford to plan elaborately, and act slowly and patiently, until just the right moment for bold action arrives.
Persons who have time to learn about their victims thoroughly (and even befriend those they're about to swindle) often enjoy great success as kidnappers of nobles (seizing heirs, loved ones, and even heads of houses, for ransoms) or manipulators of nobles, guildmasters, and "big fish" merchants such as shipping fleet owners. Manipulators often seek rich offices and titles for themselves, or the adoption of official policies that will enrich them (thanks to the holdings or businesses they've already acquired). For example, getting a king to urgently desire a navy is going to enrich the only local and reliable suppliers of sails, rope, timber suitable for shipbuilding, as well as shipbuilders. Control most of those, and any available suitable vessels that could be purchased for the beginnings of a navy, and your fortune is made.
Manipulators work patiently to "steer" rulers, or heirs of rulers, or sequences of decisions, to their eventual benefit. They often spend funds subverting persons of importance, not just through bribery and blackmail, but often by the more subtle befriending and gifting method. More than one noble of Cormyr has done the latter well enough to have courtiers volunteer warnings of coming raids or investigations, out of a sense of obligation to friends.
Manipulators often arrange long-term, circuitous roads to riches for themselves, such as joining business consortiums and then arranging "accidents" to befall their partners, keeping these as "innocent" and slow in succession as possible to alleviate suspicion. However, far away from all the deaths and bad luck, they move step by inexorable step closer to inheriting all, or winding up in control of something they started on the fringes of -- something that now holds financial power in a land, city, or region.
Some manipulators in Amn have even secretly achieved near-monopoly of the supplies of certain goods in an area, so they can oh-so-slowly fix (raise) prices.
One of them did this so deftly that when he fell on hard times and a rival tried to ruin him by getting laws passed forcing him to sell his businesses, he (sobbingly) sold them to himself -- or rather, to half a dozen rival firms that he, through successions of several "front men" who knew nothing of their ultimate boss, was behind.
Really good manipulators who befriend nobles often end up as trusted confidants when they start to ruin those same nobles: unaware of who their true foe is, the noble turns increasingly for advice and support to his "trusted friend."
Liches and other undead often need to manipulate others into retrieving items from their pasts, or freeing their servitor creations -- and all manipulators find it useful to hire adventurers and commoners to do "dirty work" and to provide them with fodder who can be framed for the manipulators' crimes when the truth starts to come out. Manipulators often find the strategic spreading of rumors to be weapons far more effective than sharp knives wielded in alleys.
Good manipulators always plan a way out if things go wrong; many of them have preplanned their own staged, false deaths, so they can simply "vanish" and escape retribution. Moreover, rumors of a vanished but lurking outlaw can be a powerful weapon against a ruler, or (through fear) force people into certain preparations or even flight. In the early days of the Zhentarim, Manshoon spread rumors of his own death several times to see who would do what in the struggle for control of the Network he had built. Not only did many rivals weaken or eliminate each other, he could pounce on those who did foolish things after he reappeared from hiding (where he had watched everything).
As Storm Silverhand often tells young Harpers: "We chase and shout after the man who steals your basket of eggs. The wiser thief is the man who manipulates us into buying goods we need at his shop and overcharges us a copper piece every time he can. He takes much more from us all, without ever having to run anywhere or suffer our anger. Indeed, sometimes we praise him for providing what we want or need, and never look past his welcoming smile."
Learn more about villains in Champions of Ruin, a Forgotten Realms supplement.
About the Author
Ed Greenwood is the man who unleashed the Forgotten Realms on an unsuspecting world. He works in libraries, writes fantasy, sf, horror, mystery, and even romance stories (sometimes all in the same novel), but he is still happiest churning out Realmslore, Realmslore, and more Realmslore. There are still a few rooms in his house with space left to pile up papers in . . .