KDramas are full of sidekicks - I doubt there is a single one without one or even two (one to the male lead and one to the female lead) or several (yes, they come in hordes, see in i.e. Rooftop Prince). Well, I'm not sure that also goes for all sageuks, though. However, most often, sidekicks are there for comical relief, and they are often stereotypical goofy best friend characters. Frequently, they take the form of secretaries to the (chaebol) hero in modern day dramas. They may also provide a specific place for meetings between hero and heroine, i.e. when they are owners of a restaurant (like in I Do I Do).
Below is my personal sidekick hit parade:
No 1: Im Ji-Kyu as Kang Woo (in Queen of Reversals)
Queen of Reversals is a drama I most certainly wouldn't have watched if it didn't have Park Shi-hoo in it. But it has. And he is so incredibly wonderful in it. Ah, I miss him so!!! Sorry, off-topic. Next to Park Shi-hoo, who plays a chaebol-son dickhead (Yong-shik), is his secretary, Kang Woo. If you've seen the two, you'll agree with me: Kang Woo deserves the gold medal in the category of sidekick, forever and ever. The way they banter and frolic and snap at each other is pure delight. No other secretary-spoilt brat pair has ever gotten close to them.
Sample Dialogue 1:
KW: You’re an outcast. Do you have any friends, other than me?
YS: Are you my friend? You work for me!
KW: (pause) Mmm-hmm. Yep, no friends at all.
Sample Dialogue 2:
YS (infuriated): Did you get my new cellphone?
KW: It slipped my mind. Today was a busy day.
YS: I’m firing you first!
KW: Ooooh, scary. The world really is about alphas and betas…
YS: Don’t say that!