You need a Big Damn Villain.
A Big Damn Villain (BDV for short) has attributes that lesser villains just don't have due to lack of recognition by their peers (look at Spider-Man II and III vs. Spider-Man), a lack of power or a lack of will. They are iconic; you are in no doubt as to who you're dealing with even if you know almost nothing about them. The gentleman in the picture is Dr. Szell from Marathon Man and he fits our criteria to a tee.
Big Damn Villains have these particular characteristics.
Fear - An element of the BDV is having other characters respond fearfully. Take Voldemort from Harry Potter; everyone is afraid of him because of his deeds, his loyal and secretive followers, his use of evil magics to kill, maim and drive mad yet you don't meet him until Book 4 of a 7 book series. See also Keyser Soze from The Usual Suspects whose reputation precedes him even if nobody is quite sure exactly who he is.
You don't even have to be secretive as the previous two examples. You can be in your face like Vlad the Impaler, the Joker, Hannibal Lector or Lord Soth. None of those individuals can be said to have shrunk back from their villainy or been ignored by those around them. As Machiavelli notes, it is better to be feared than loved since:
"...fear preserves you by a dread of punishment which never fails."Opposition to moral values - The BDV has beliefs opposed to what is good and just and acts on those beliefs in ways which shape the world. The Zhentarim in the Forgotten Realms are a good example. An organised trade cartel who subjugates customers and seeks to recruit them into an oppressive regime that serves an evil god. Did I mention they have evil wizards who ride gryphons and backing from devils as well?
Before spiralling into moral relativity, note medieval definitions of good were different from today but this can work if the morality contrasts with what is normal - an example in Pendragon, there is a scenario where a knight filled with a passionate hate of Saxons draws the player characters into a lucrative raid on a Saxon village during a time of invasion. Yet this knight goes over-the-top. What do the knights do? Do they declare "War is Hell" or try to stop him?
Persuasion - The BDV needs to be able to draw others into their plans. Jigsaw from the Saw films does this by abduction, placing them in deathtraps. Others do it with incentives, offering rewards for dubious behaviour. Arguments and rhetoric can also make ordinary people act in evil ways - Hitler's Germany is an obvious example. Equally Iago from Othello manipulates Othello and his company into self-destruction and hatred of each other.
Other persuasive villains include Preacher Harry in Night of the Hunter and Richard III, whose rise to power combines political rhetoric, smear campaigns and assassination. Keeping with the Shakespearean for a moment, Cassius in Julius Caesar is a tragic manipulator, tempting Brutus into assassination. In Gormenghast, Steerpike manipulates and insinuates his way through the court until he gets within striking reach of the Groan family.
Power - These villains need to be able to shake things up. Power can take a number of forms but the BDV doesn't limit themselves. They can be legitimised by government or may even be the government (the Northfire party in V for Vendetta). They can have the raw power to coerce those around them to comply (e.g. Magneto in the X-Men movies). They may have knowledge that lets them challenge anyone around them (e.g. Lex Luthor).
Commodus in the movie Gladiator has the Roman Empire behind him, having power of life and death over Maximus. In Firefly, the Operative is sanctioned by The Alliance and he chooses to use murder, intimidation and threats of rape in order to find and retrieve River Tam. Another Firefly example previously mentioned here is Adelai Nishka, who tortures Malcolm Reynolds to death and back again just to get some information.
Resolve- So someone asks you to stop. Do you? A shame, considering you've come this far, gathered like-minded individuals to your side, engineered an insidious plan, prepared for the great moment only to back down on the word of a protagonist. Unless your hero is intimately aware about what makes the BDV tick and is sure that such a strategy will work, it's going to be at best a stalling tactic and at worst, give the BDV a really clever idea.
For the Forgotten Realms again, Artemis Entreri, an assassin who is emotionally dead inside; Vito Corleone in The Godfather doesn't shrink from the consequences of his orders, nor does Hans Gruber in Die Hard - it may even be a matter of principle for the villain. Consider Angel Eyes in The Good, The Bad and The Ugly:
"Problem is... once I'm paid, I always see the job through. You know that"