There is some serious mystery going on with resident mob boss/super chef Master (aka Cha Seung Pyo), and he is truly a fascinating character. From the beginning his motivations have been hazy, and his background is definitely shady. There's a big secret regarding his true identity, and I think I know what it is.
If you don't want spoilers up to episode 10, don't read on.
Let's start with what we know so far. Master is good with knives. He's mentioned it on multiple occasions, and not just in the "I'm a chef, so I know what I'm doing" kind of way. We finally saw the darker side of that skill in episode 9 where he took on the gangsters and threatened the boss who was foolishly trying to interfere in Master's business.
We've also known for a long time that Master is the true loan shark behind the bumbling Enforcers. Yet that seems to be a vital secret to him, and the three of them are constantly working to hide their relationship (although, if the Enforcers were less inept, they'd stop calling him Boss all the time).
Master also has a suspicious interest in Gong Min Young, which the Enforcers constantly point out by remarking on how he's lowered his standards. I'm pretty sure that his interest started out as a way to get back at Seo Byung Hoon (more on that later), but has morphed into a genuine attraction to Min Young, mixed with some vengefulness now that she's rejected him. That vindictive spirit seems to be directed at Byung Hoon for now, so I'm not too worried about Min Young's safety just yet.
Now, there are just so many things we don't know about Master, but these things seem to be important. Why does he lead a double life? Why is he keeping such close tabs on Byung Hoon and the Cyrano crew (because it's clearly not just about the money)? Why does he seem to know things that he shouldn't?
Here's my answer: Master is really Go Do Il, Byung Hoon's childhood best friend and the man who was engaged to Byung Hoon's first love, Yoon Yi Sul. I'm pretty sure he faked his death and has been following Byung Hoon all this time.
Why do I think this? Well, for starters, Master seems to know much more than he should about Byung Hoon and his past. The two men clearly aren't close friends, and Byung Hoon is so closed-lipped about his past, making it improbable that he would ever have confided in Master about his early scars. It's possible that Master could have spied on Byung Hoon and found some things out (like Min Young was able to with the slideshow), but his knowledge seems more personal than that.
Also, there was that sinister comment Master made when Min Young asked how to end a love triangle without hurting someone. "One of them has to die." He said that after explaining to the enforcers that Yi Sul was Byung Hoon's first love, and the girlfriend of Byung Hoon's best friend growing up. Again, not really something Master should know, and especially not something he should seem so bitter about.
But, if Master were really Do Il—years after faking his own death—it all makes sense. At least in my brain. In the flashbacks, Do Il seemed to idolize Byung Hoon, and seemed to understand his friend's feelings for Yi Sul.. If he already had ties to gangsters when he "died," it would be a strong motive for him to change himself completely, and while he was a good friend, I don't think he was crazy enough to fake his death just to take himself out of the love triangle. That was probably an added benefit or an unplanned consequence of his decision, but it's one he's clearly come to regret.
I remember Master saying something earlier about changing appearances, or plastic surgery, or something along those lines. Although I can't remember the exact quote, it was just another clue that seemed to click. Clearly, he'd have to change his appearance if he was going to spy on his best friend, especially if he was seeking some kind of convoluted justice/revenge.
If my theory holds true, Master seems quite angry towards Byung Hoon over his crush on Yi Sul and Master's own inability to be with her. He set himself up in the next building so he could conveniently watch the comings and goings of the clients of Cyrano and see if his erstwhile buddy ever made a move on Yi Sul. He also secretly became Byung Hoon's creditor, giving him plenty of excuses to scare him (while watching innocently from below), and reasons to send his Enforcers inside the theatre to keep tabs on the happenings there.
And although Master has severed his ties to Yi Sul and (probably) buried his feelings for her, he couldn't resist the opportunity to thwart Byung Hoon further by interfering with Min Young. I think he initially ingratiated himself with her to get in Byung Hoon's way after noticing their chemistry. He liked her enough, but wasn't romantically interested. (It was pretty obvious that he knew Byung Hoon was outside when he opened the window to ask Min Young to go out with him, for example.) However, as his involvement grew, so did his attraction. Even though his first inclination was to use her, I think he's genuinely falling for Min Young.
So, asking Byung Hoon to help him win her over is not only his attempt to follow his heart, but it's also a great chance for him to crush Byung Hoon in a very personal way, using Byung Hoon himself to do it. It's clever and convoluted, and really really evil. But it's also a really compelling twist in this story that just keeps getting better.