I've been watching a lot of Suits lately, and I'm struck by two things. The first is that Gina Torres must have something in her contract about a full body shot every episode showing off whatever gorgeous outfit she's wearing, and how many hours she's put in at the gym. The second is that Louis Litt, played by Rick Hoffman, is a fantastic villain. I think he's a fantastic villain for several reasons, and perhaps the fact that he's lamp-shaded as something of a Shylock-ian Jewish lawyer obscures them. The first is that he's sympathetic. While the audience may wish to have Mike's perfect recall and intelligence, or Harvey's style, good looks, and smarts, Louis is the one that doesn't have those things. He's unstylish, unaware, vain, needy, rude, and clueless. It's all his faults that make him sympathetic, even when he's on the wrong side of the table from the heroic team of Mike and Harvey. We're not rooting for him like we are rooting for them, because we don't want to be like him; we're already Louis Litt in little ways. It's these moral failures as a result of pettiness, or jealousy, or pique that makes them relatable, and also villainous.
Note, for example, that Harvey Spectre is a dick. However, he is a handsome, capable, confident dick. Part of the drama of Suits depends on Harvey being knocked down a peg or two every few episodes, meaning that the problems he faces each episodes don't feel formulaic because he doesn't always win, and retains both the willingness and ability to overcome so long as he can stoop low enough. I would like to say that the Harvey character is redeemed by his moral code of loyalty, but it's precisely that loyalty, to Mike, to Donna, to Jessica, that means that he's flexible in other areas, like hiring Mike to be a lawyer. Again, it's lampshaded in the series that Harvey is the scumbag that Louis wishes he could be, because Harvey gets away with the stuff that would get Louis fired or worse. Indeed, he gets away with what eventually gets Louis fired, and then re-hired.
Harvey is the hero in the ancient Greek sense, rather than in the modern Christian sense of someone sacrificing himself for others. He's a hero in the sense of someone who is powerful, and blessed. His moral achievements are those of a Nietzschean super-man, overcoming the morality of the herd to win at the game of law. Louis' moral failures make him an excellent villain because they are both in keeping with his character, and a result of moral weakness. He does the wrong thing because he thinks he can get away with it, or because he thinks he can get some sort of advantage, or simply because he gives in to temptation. He's not doing anything out of a sense of malefic intent, except when that derives from some deeper sense of outrage, or prudence, or similar error in judgement. Louis is villainous not because he's evil, but because he fails to do the right thing when needed to do so. The character of Louis is a great antagonist for the character of Harvey precisely because they both mean well in the context of supposedly high-priced corporate lawyering, and one brashly succeeds where the other invidiously fails.
It's something to consider, I think, when writing villains. In particular, and perhaps this is an odd turn, it's worth considering in terms of writing villains for Warhammer 40,000 stories. Aaron Dembski-Bowden's Night Lords trilogy, and a few of his Horus Heresy novels, manage this somewhat in making the protagonist both villainous, and sympathetic to degree or other. In Warhammer 40,000 novels we see characters that are more like super heroes or Greek heroes than in less fantastical fiction, and frequently that means that the stories devolve into a kind of sloppy myth-making, where the mythic becomes mundane, and the characters one-dimensional and interchangeable. ADB manages to avoid this somewhat, if not altogether, and I suspect that there's at least one character in Warhammer 40,000 that could be said to be a great villain or hero, not because the story tells of us the mighty feats or accomplishments that character putatively achieves, but because of the journey that character takes on the way, either overcoming a moral weakness, or succumbing to it. I think Dan Abnett tried to do this with Horus in Horus Rising, but there wasn't enough written about Horus to make him sympathetic or even much of a character before he faces his calvary-moment, cries out to his father, and falls. Likewise, in The First Heretic, plenty of time is spent developing Argal Tal, although not to the degree that one could say what he would do except salute his Primarch and follow orders. Likewise we are supposed to see Lorgar's fall through the fall of his subordinate, but again it's not that Lorgar and Horus are supermen that makes them unsympathetic, it's not that they haven't faced the kind of hardship that ordinary men might face, it's that we as the audience don't see them develop. We don't see them do things they don't want to do so that those actions and choices can foreshadow the villainy to which they descend.
I feel that if you want to write a story about a man's descent into villainy, you first need to show that he wants something. Then you need to show how wanting something similar means he fails to achieve a goal. There has to be a conflict between goals such as being the good man and getting what he wants, and that conflict has to be the culmination of several such conflicts so that his decision, the wrong decision, makes sense from the perspective of that character. I think that's why I like the novel Knight of the Black Rose, which is also a tacky little genre novel that I love. In it, the titular Loth Soth, damned to undeath after failing to save the world in order to punish his wife for his infidelity (after killing his previous wife to marry her...), likewise betrays his commander so that he can trap her in undeath with him as a companion. Instead, he's spirited away to the semi-hell of Ravenloft, and he's motivated to escape so that he can be re-united with the woman he's attempting to drag down into damnation with him. Of course, this need to punish disloyalty, perceived or otherwise, comes back to bite him. Soth's opportunity to escape from Ravenloft is thwarted by his pathological need to punish the disloyalty of the ghost of his seneschal. He eventually escapes, several books later, due to issues of character ownership between the original authors, the publishers, and the authors 'borrowing' the character. But story-wise it's good because Soth's motivation is explained, his struggles shown, and while he undergoes something like personal growth, his final decision is the wrong one because rather than using that growth, having had to trust and rely on a set of companions, he visits vengeance on an old one.
Of course, there's a reason why Suits is prime-time television programming, and these genre novels are, well, genre-novels instead of prize-winning literature (even if some of it is indeed best-selling). The production has the opportunity to fund better writers to do better writing, because that investment is worth it for the advertising dollars that it buys for a wider audience. One could say that the writers make better choices than the authors of the novels precisely because they have the opportunity to do so.