Well the killer finally got a face in episode 9! 
I officially give up trying to guess anything in regards to this drama now. :p
Hi all,

Here I am after episode 9 and reading this thread for the first time. You got some interesting theories here, and all make sense. Is the killer KC himself? Is the killer the negative alternate of KC? Some food for thought :)

While reading you, a sentence from Harry Potter came to my mind:

[FRAGMENT FROM BOOK 5]
"The one with the power to vanquish the Dark Lord approaches... born to those who have thrice defied him, born as the seventh month dies... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives... the one with the power to vanquish the Dark Lord will be born as the seventh month dies...." — Sybill Trelawney's prophecy made to Albus Dumbledore
[/FRAGMENT]

This sentence applies to W. At the bridge both of them (KC and the killer) came to life because YJ's father wanted to take away from them their purpose. KC's is to find the killer and the killer's one is to know who is he.

It seems that we all agree that the killer is alive and has free will. The problem is that he is way more powerful than KC because the killer knows that he is inside a webtoon. In this episode we saw him teleporting to the broadcast station using the drawing of a door. I think that the problem is that Yeon Joo only erased the memories of Kang Chul, and not the memories of the killer. She should have drawn the killer inside the webtoon in a scene happening just after Kang Chul was stabbed. But at this point, unless she draw the killer getting into a car accident and have a big memory loss (and the readers wouldn't accept that) there was no possible way to remove these memories from the killer.

What I don't understand is how the killer could steal Sung Moo's face in real life. How can he get it back? How can a character (that has a free will) steal the identity of a real person?

Let's see how it goes.
What I don't understand, how does the killer even has a personality? Coz he wasn't created with one. Not like Kang Chul was. Kang Chul himself said that the killer does not feel remorse nor sadness coz he doesn't have a personality, he was created as an empty character just to kill KC family. But then he does feel anger somehow? I myself think it's just a small mistake from the writers of the show but still it bugs me somehow... 
Lol no need for speculating. That shit's already out. Logically, the killer was created by the father. It's his webtoon for god's sake. There's no need to speculate.
I drop all my theories because this drama is too crazy!!! hahahahaha God knows I love it to the core! 
@ Kate : The point is he doesn't have a personality. But just like Kang Chul, he witnesses all the incoherences in his own existance. He is always appearing out of nowhere and might wonder why he's acting that way and why he doesn't have a face. The one thing the readers of W know is that he's always keeping an eye on Kang Chul. So, when Kang Chul enters the real world, he follows him as a matter of course. And that's when he learns that he is a comic character as well. One without an identity. That's how I interpreted it. Hope it will help you.