Antagonists

The antagonist doesn't have to be a "bad guy" merely an opponent of the main character. Accordingly, though I don't know of any specific books on the subject, I would expect you develop them just like you would the "protagonist" and then put them in opposition. After all, the protagonist is in opposition to the antagonist also - for every action, there is an equal and opposite reaction. If you can do one, you can do the other. My ten cents (inflation) for what it's worth. Take care. Vern

I have several books that address the topic, but it’s not a “book length” topic in and of itself.  Just Google "how to write a great antagonist" and you’ll find plenty of solid articles and blog posts to bury yourself in.

For me, motive would flow out of character, and the style of action would be determined by the motive. I suggest writing a biography of the character or a shadow plot with him as the star to see what he does.  As to why he's opposed to the protagonist, that can be anything--from being mad that the main character saved his life at the expense of his hair (Lex Luther and Superboy) to not understanding why the protagonist is doing what he's doing (Dagney Taggart vs John Galt) to the horrors of war turning a good man bad (Black Jack Randell vs. Claire Beachamp).

Lex Luthor is an example of how you can deepen the character's motive based on his character. In the latest incarnation, he fears for the safety of his planet, has self-esteem problems, so he hates Kryptonians and is anti-alien. He plays on the insecurities of others and his own sense of irrational inferiority drives him to destroy those better than him and to be a world dictator. It's easy to see what his motives are for destroying Superman, Supergirl, and Argo City, and his attempts at world domination. This leads to his theatrical style, using classical music as a background to his escape from custody. And that, in turn, gives his style. Yes, a graphic novel/TV series example, but it's illustrative.

We have to keep in mind, too, that a protagonist is the first mover of a story, the antagonist opposes him. This is important in understanding motive. In Atlas Shrugged, the book is mainly written from the antagonist's POV. Other POV's are present, but they dovetail into her. You find yourself rooting for her. The protagonist is vaguely felt and doesn't make himself known until way into the book. In Heart of Darkness, the antagonist is within the character of the protagonist and the reader is wondering about his motives until faced with the horror. (Something repeated in the movie based on it, Apocalypse Now.)

Sometimes, the antagonist is a whole system. Claire, in OUtlander, is constantly thwarted (at first; haven't gotten very far) in her goal to get back to her own time. Circumstances are the antagonist until BlackJack Randell graciously decides to fit that role. Then, his motives are brought out--he has experienced the heart of darkness and gone over to the dark side (how's that for mixing literary metaphors?) He's till a patriot, though, and is motivated by a desire to find the Jacobites.

The antagonist and the protagonist could be good guys, both working for the good, but at odds in how to achieve it. The antagonist might think the protagonist is the villain, only to find out (usually, almost too late) that he or she isn't.