Villians, But Can't Help But Love

*Spoiler Alert* (picture links only)

We know Jang Han Seo (the head of Babel) is working under someone, however the show does not reveal to you who that person is until later in a great reveal. There were articles and more that told some people who that person was, but I'm going to try not to spoil anything... but if you don't care, there are links you can click for pics/gifs. 

The actor does a great job of portraying this duality of the character's acting, and his extreme terrifying craziness. He has Han Seo shaking in fear because of him, and he's not afraid to intimidate others. There's time when the viewer knows who he is, but our anti-heroes still don't, allowing for fun and not over done dramatic irony, and fun scenes where the actors has to play a little of both his character's sides.
He plays a perfect foil to Vincenzo, forcing him to have to meet his mafia side he was trying to hide. Making him become a monster to destroy a monster, and it's a wonderful battle of wits and how far the other is willing to go to achieve their goals. Because our villain is so good, our anti-hero is able to show off just that much more.

*Spoiler warning? (You learn Ep.1 who K is, but the way they introduce it was pretty dang fun and cool, and I don't want to take away from that in this >.<*

Similar to the main villain in Vincenzo, K is the perfect foil for Koo. As stated by Koo's husband Koo and K are very similar people, which gives the two an almost Sherlock vs Moriarty feel. They enjoy the chase of each other and the challenge it lends to them. However there is one main difference, K loves killing.
She has rules for these killings, which leads the audience, while still not okay with her actions, to almost sympathize with them anyway. Her victims have done horrendous things as well, and are the type of people commenters online would say don't deserve to live, so K fulfills that wish.

So we can't actually hate K ever throughout the show, if anything we feel pity for her, that is, when we aren't impressed by cunning. It's her cunning, after all, that makes Koo's problem solving that much more impressive. Also she's dang cute, if not also terrifying.

Though, while she's definitely the main villain, she is not the main antagonist.
Can't forget about her sidekick!

Scorpion King! Oh Scorpion King. How can someone kill so mercilessly, and look so innocent and cute directly after? (I successfully made my first gif lol)
Honestly that's the moment the actor sold him for me. Scorpion King is merciless, and quick witted in ability to turn the ticking explosive ghost valley against itself and use it to help his father's plans. While wishing for his father's love and approval, he is himself his ticking time bomb, and will turn on him if he needs to.
He is a wonderful mixture of heartless killing machine (I mean he IS leader of assassins...) and a cool, collected (and cute >.<) leader.

Everyone in this drama has their own stories and aspirations. They each have their own ways of trying to hit those aspirations, causing a lot to but heads, and at the top of those people affecting our heroes' lives is Tagon. If fact if he weren't the cause of the main characters' problems, he could be his own protagonist.

Tagon is loved by the people, he was sent out by his father to fight for more land, and enslaved other people not part of the main three tribes to make life easier for the people of Arthdal. He is their war hero, and his father's biggest fear. Tagon grew up surrounded by plots and his father killing anyone to keep secrets, causing Tagon himself to have warped morals. However, while willing to do anything to obtain power, he tries to avoid bloodshed to get there. Taehala a person of also warped morals, the two stand together in their understanding of the other's cruelty and will to survive no matter what.