To me, the best antagonists in fiction are those that have real motivations and consistent abilities. They’re driving at their goal because they have a core belief that they are in the right, no matter what society says. They don’t suddenly teleport out of nowhere because plot requires them to, they don’t have all-perfect knowledge of the protagonists’ plans, and so forth.
In my most recent Legend of the Five Rings campaign—a five-year saga where a single “bad guy” was behind (almost) all of the party’s woes—I tried to ensure that my antagonist, no matter how twisted or powerful, was beholden to the same mechanical rules as the PCs and that his methods all supported his end goal; that from the outside, his actions would appear at least logical, if not reasonable.
After the party had interrupted one of his minor plans in the opening adventure, he decided that he wanted to see who these would-be heroes were, and arranged for them to be invited to the same prestigious party he would be attending. Ingratiating himself to the party, he soon became a close confidant, particularly when measured against the other, often distant, members of his family. In time the party came to trust his advice, or at the least regularly keep in touch.
Thus began a years-long repeating cycle of them writing to their “friend” about their expected upcoming travels, only to find that the object of their search had been moved, or specific individuals had been made aware of their impending arrival. One or two times the party had to change direction quickly, without the benefit of writing friendly letters prior, and in those cases they actually caught up to or overtook the plans of the mysterious and shadowy figure whose aims they were hoping to thwart. Pleased with their victory, they would often write to their allies to give them the details. Details the antagonist used to ensure his other plans wouldn’t be so easily stopped.
It was only in the final months of the campaign, with years having gone past both in- and out-of-character, that some in the party started to put the breadcrumbs I had lain throughout the entire story together. I remember the specific moment when one of the players figured it out (even if her character hadn’t), and the stony look she gave me from across the table. It was such a rewarding moment as a game-master, to have had a consistent and continuous thread woven through the larger story of the game world.
At the end of the chronicle I invited the players to ask questions about the campaign, to put to rest any lingering doubts or hanging unknowns about the game that we had enjoyed over the past five years. Most of the questions were about when and how the “big bad” prepared for their various investigations, and I was genuinely happy to have an answer for almost all of them (of course some particulars get lost in time). Because I had an internally-consistent, believable antagonist, I was able to construct an empire-wide network of foes for the party to deal with, with realistic layers and internal politics, all while keeping a consistent theme for the whole game.
Though the new campaign I have spent the past year planning doesn’t have the same sort of organized enemy the last one did, it’s still important for me to follow the same guidelines I used for the larger conspiracy in the upcoming smaller ones—characters need reasons for acting how they do, particularly when their actions fly in the face of tradition or societal expectation. Being random for random’s sake isn’t ultimately fulfilling on a narrative level, and honestly makes it harder for me to end up with a cohesive plan unless there are understandable steps from A to Z. Obviously every writer, game-designer, and story-teller operates in their own way, but for me I’ve found that holding to these simple ideas goes a long way to building a realistic and believable world for others to invest in.