so anyone want to start speculating on who the killer is in the webtoon? I have bets on it being her father. He started the webtoon on that premise, so he became the killer. And that's why every time in the webtoon, the killer is shrouded and you don't see him. If it's true, can you imagine what kind of wrench it would throw at the plans for the romantic plot line? Oh, the writers are making me really exited to see what they come up with!! This is shaping up to be an all time favourite!

OMG I thought that I'm the only one who thinks it's the father!!
To be honest, apart from knowing that the father wants to kill Kang Chul indirectly. I think it's to early to speculate who the real killer is.
Based on the information so far, it could be one of the Olympic Contestants, trying to get revenge because of jealousy or whatever since he was able to win the Gold Medal on his first attempt whereas the others seem much older & would think that it isn't fair or whatever, or it could be the Prosecutor, who wanted fame by trying to put him away since he was such a famous role model for young people, or Kang Chul, himself, possibly having multiple personalities or whatever, hence why i said it's to early to speculate hahaha
I agree it's still early to formulate suspicions, even the exit-entry rules aren't fully established yet. But it's interesting to know that Kang Chul discovered something out of his world is happening that is beyond his control yet so obviously focused on targeting him, lol. Anyway., one thing is for sure, it will keep you thinking, like Nine did. :D I wished Kang Chul wasn't really a cartoon character in the end created for a manwha, because what, it will be romantic tragedy. I don't want to! hehe
My guess is the father and/or the prosecutor from episode 1. And yeah it's early days to even start speculating who the killer is but I'm a just list my top two before the drama unfolds more suspects.
I think we haven't met the killer yet. I agree with the poster who said it could be one of the olympic contestants, but at this point, I have no idea *shrugs* I think it's unlikely tht it's her father tho..
The killer stalks Kang Chul into the "real world"
Indicating even if the father had created him to begin with, the killer has taken on independent thought
Or...the father drew him coming out of the manwha world and offing Kang Chul
Betting my cards on the Dad is too early. I have a feeling there's more of a twist here. What if it's really a different dimension where in other people could meddle more into Kang Chul's life. Just saying... there could be other culprits besides the obvious like the father or the prosecutor. >_<
@Kachiling thts very interesting, but how do u know about this "spoiler"?

I agree with @biniBningPunkista. But thts a super interesting theory u have there. How much more awesome could this drama get? Wow, I'd nvr think about other dimensions being able to get into Kang Chul's world. But I have thought about Kang Chul entering the "real world".
I think father being killer is too... obvious? BUT we can assume from Yeon Joo & her father conversations that he did went to W World and met Kang Chul. But he was never mentioned in the manwha (since come on, Yeon Joo would probably notice that there is a character extremely similar to her father and would mention it at some point). The only character we know about that met Kang Chul and is to some extended unidentified is the killer... + the time her father went missing is the time someone tried to kill Kang Chul. Since the manwha and characters in it start to have their own independent thoughts and take independent actions despite what Sung Moo draws MAYBE he's not a killer BUT he goes to W World and works with the killer to get rid off Kang Chul. 
Truth to be told, after only 2 episodes... anything is possible. I don't think the killer is one of the contestants tho, they would stop after killed Kang Chul's family and not hunt him for next 10 years. It just doesn't make much sense. I would rather lean towards the possibility of prosecutor being involved for two reasons: losing Kang Chul's case after trying to get him a sentence of death would be a deal breaker for his career that he would never be able to work around anymore, he would be done so the revenge makes sense. AND producers of dramas just love to make prosecutors a bad characters. IF prosecutor is not a main character, than he is most likely an asshole or even a villain. 
I also think the father is too obvious a choice. I could see the prosecutor being the killer, but I think this drama is too creative for tht. 

This is what I'm thinking.. Maybe it's another version of Kang Chul that is the killer! Thts how he was able to get a hold of the gun, thts how his fingerprints were on it! 

Idk, have u guys ever seen the movie The One with Jet Li?? I think maybe something like that may be going on. Maybe an alternate version of Kang Chul found a way into Kang Chul's world and killed off his family? But what would be his motive? And if thts the case, why would the father create something like tht. He did say tht he didn't know tht he was creating a monster. Maybe Kang Chul turns into a monster, and the father wants to kill him off before he has the chance to turn into one. But if a future Kang Chul is trying to kill a present Kang Chul, wouldn't he essentially be killing off himself? Lol I'm so confused. Idk, but I think it's gonna be some twist where another version of Kang Chul is the killer. I think thts why his family was so shocked before they were killed. 
I've done some thinking and honestly, I don;t think the identity of the killer is even important. I don;t think we will EVER know who he is. Coz at the end of the day the mastermind behind Kang Chul's family being dead IS the father. And now that Kang Chul is more aware of his surrounding and that there is something that tried to ruin him/kill him and can influence the world he lives in... the revenged he wants will be on the Sung Moo. The killer was just a pawn, a plot device. And the moment Kang Chul figures it out (and we all know he will), he'll go after his true 'enemy' aka Yeon Joo's father. + it will give the love line more dramatic turn. So it kind of fits? 
I'm still going to say this but its still WAY to early to know who the actual killer is hahaha
But @khjfan01 that idea of having another version of Kang Chul is an interesting one, & yes ive seen ' The One ' like i also said, he could " Kang Chul, himself, possibly have multiple personalities or whatever, " that he doesn't even know about, so in a sense its going on a ' similar line ' as you are on hahaha
The reason why I don't think it's the 'multiple personality' type of think is: it would changed the genre of the drama since it would add the psychological aspect here. and it would be too much? you already have melo, fantasy, romance, crime, medical...  same with alternate version of Kang Chl, because what you do with him later? kill him? you need to somehow end the story of that alternate version. If he came from 'the real world' how come no one ever notice the dude that looks EXACTLY like the main character of the Korean sensation webtoon that everyone talks about? in the age of everyone talking selfies and random photos and instagram etc... someone would post a photo of his on the internet sooner or later. and if he is not alternate version from 'real world' than were did he come from? from yet another alternative reality? that would make it 3 different realities in one drama. I think it would be to hard to maintain and make it work. + there is yet another possibility: the person who killed Kang Chul’s family is not the same person that tried to kill him on the roof. The 2nd one MIGHT be the author using his own plot device (aka the killer he created) and dressing the same way the killer was dress to kill Kang Chul. But then why wouldn’t he just draw that? why would he risk going into webtoon and getting himself in danger? + in the preview of 3rd ep we see some fighting scene between killer and Kang Chul and I doubt that Sung Moo can fight like that, he is kind of old and he’s just a comics writer after all.
Obviously it's early and all the speculation are far fetched but that's the whole fun in it. Later when we get more 'clues' we can compare them to all the theories and laugh at how wrong we all've been hahaha it reminds me of Who Are You: School 2015. There were some CRAZY theories there after 2 episodes were out hahahaha hahaha 
@Kate, I ttly agree with u about tht being the whole fun it speculating! It's such a good thing to discuss and speculate early on, so then we can look back and maybe even be able to speculate more until the ending. I really do love reading the different perspectives, it makes me think about what I haven't, and maybe I can grow in my thinking tht way. 

Now, what u said about the person who tried to kill not being the same person who killed his family is one of the possibilities I was thinking of. Tht may very well be the case. I disagree about we never being able to find out who the killer is. I think we will. 

I see what ur saying about how the father essentially IS the killer because he wrote it tht way. But I don't think of it tht way. I think the father did indeed write Kang Chul's family being murdered, but it wasn't malicious. It's not like he knew his work was going to come to life. He was just writing a story for all he knew, he was letting his creative juices flow. What I wanna know is WHEN did Kang Chul's world start to come to life. It could have been sometime before we saw Yeon Joo go into his world. Or, when the father got pulled into tht world, he could have been there for a really long time and thts when he made his decision to kill Kang Chul. But then again, Soo Bong said tht the father was planning on killing Kang Chul BEFORE he disappeared. So I think once we get a time frame for when Kang Chul's world first started to take shape, we'll be able to piece more things together.

I also don't think it multiple personalities. I don't think it's anything psychological at all. More alternate universes is a little far fetched, I know. Maybe it doesn't have to be more than 1 alternate universe, all I'm saying is tht I think it's some version of Kang Chul. Something tht the father created, so I guess if tht is the case, he didn't have to come from another alternate universe. But the more and more I think of it, I think there's another version of Kang Chul.