These two guys here man, I tell ya

You know, its wierd, I notice these two guys seem to show up a lot in the shows I like, but, surprisingly, they're never technically "important" characters,    This Guy  tends to show up in a lot of shows I watch as one of, if not the, primary antagonist, and This Guy tends to show up frequently too, usually as a slightly larger minor character, typically on the friendly (or at least not antagonist) side.   They both play their roles well, and definitely contribute to how good the show is, even though at least one of them doesn't really play "important" people, those shows still wouldn't be the same without them

There are a lot of guys and ladies like that :D ... they usually play eunuchs or mums or ministers etc. xD

 Knavery:

Where is the evil Korean guy. The guy always playing the CEO with a violence problem and hiding criminal behavior. He's usually the dad for the second male lead.

Sounds like you're definitely talking about Jung Dong Hwan, who is the first "This Guy" in the original post.  He's almost always some relatively powerful figure (politcal or business), and is quite often the father of the second lead