My main antagonist is more of a mystery. You don't get to meet him until toward the end of the book, you just hear about all the terrible things he has done or is doing. I don't know if that will make him memorable to the reader, but every time my MC looks at the scar on her arm or the scars on her brother's face, she will remember all that happened because of him, whether directly or indirectly.
I'll go with what `saintartaud said; I don't deal with making the villain iconic. What matters to me is how much depth I can put in him and how realistically human I can make them be. The hardships they'll face, their whole reason for existing and for doing the things they do, how they feel about certain things, quirks, personality flaws, back-stories, etc.
And well-developed villains are my favorite type of characters to create. The first villain I ever created happens to be my absolute favorite. He's cunning, short-tempered, stubborn, overbearing, sarcastic and tends to act like an absolute ass to anyone he dislikes...which is everyone. But underneath lies a lonely, unappreciated intellectual who has an inferiority complex (he acts superior to cover up his feelings of social inferiority), is afraid of failure, and his only reason for doing evil things is because he's been tormented so much for being a know-it-all and his computer and engineering skills were always overlooked or degraded. So he developed the view that the entire world was against him. He turned his back on the world and decided to gain appreciation in a more ruthless way by manipulating people to trust him and give him free reign. In other words...He just wants people to accept him and appreciate him for who he is. He's just doing it the wrong way.
I don't fuss over whether the antagonist is "iconic." I focus on the character and their role in the story, clarify their motivation and conflict with the protagonist, and work from there.
My suggestion would be to look at the antag the way (hopefully) you look at your protag: as a whole person with their own wants and desires, with some complexity and struggles, not just good or evil. What matters to your antag? What do they want that the protag won't let them have? Basically, try to think backwards from the villain's point of view. People are rarely malevolent just for the sake of it. Some want revenge, some think the ends justify the means, some don't think they're doing anything wrong. It really depends on the story and your characters.
They need to be in conflict with your protagonist -- they don't necessarily have to be anything more. If you want them to be interesting, then put as much thought into them as you do your protagonist. Define them as a person, give them flaws, and if need be, make them like a car crash. They were fine once, but now they're on a path counter to your hero's. And the audience can't look away from a good car crash -- tragedy, whether in the making (like Macbeth) or already happened (like Darth Vader) or even to come (Jacen Solo in Star Wars: Legacy of the Force), will always be attractive for an audience.
I don't think any of the "villains" in my stories are really villains or really that evil. They stand in the way of the protagonist, but that's not their main purpose in life. Well, except for one, but that guy was insane... The others are actually very intelligent.
Make him terrifying. Darth Vader was awesome because he was pant-wettingly terrifying. He could kill you with his hand. He was dressed all in black. You could not see any sign of flesh (with exceptions) and that made him almost inhuman. Also it seemed like he could and would kill anything that moved. Or tried to. He had a temper. Seeing the original trilogy as a small child made me terrified of Darth Vader. For years I would not watch The Empire Strikes Back. But now, Star Wars is one of my favourite (if not my favourite) set of movies. Make him badass. Along the lines of scary, but with more panache. Make him cool, awesome, his resources/abilities/training epic. Make his lines awesome and witty. Make him smart. Make him stick around. Make him hard to beat. This will make him epic because he is so very difficult to kill/defeat. Everytime you turn around, there is, hands clasped together, grinning like a maniac, with a white persian on his lap. Make him hurt the protagonist so much that the reader so angry that they want to kill him. All these things make him terrifying. They make him (or her, I suppose) awesome and epic. That's my opinion anyway. Good luck!
Exactly! You have to give your readers a reason to hate him, to make them more invested in the story! I always have trouble trying to invest my readers in my story, it always feels like I am the only person who cares about my characters, not that I show my work around or anything. oh well. Thanks!
What are their ambitions and fears? I always work with ambitions and fears first when creating a villain or antagonist. Those two qualities can explain what makes them ignore customs, ethics or morals. Is it something they despise in their culture or world view, is it a biased perspective, perhaps like many criminals (not all) it was an act of desperation; something they perceive or fear as a threat or hazard to themselves or purpose.
How is the villain/antagonist's character provide tension for the protagonist(s) and/or move the plot through the story? or how do I incorporate that tension into the story? That one I really have to figure out first.