i.e. What character is not a parasite in this (fantastic) movie ? TLDR : imo NONE, or at least that's what I want to believe. But i throw the question out because the two friends with whom I talked about it didn't quite agree.

Friend who originally gives the contact of the family at the beginning : check

Lee(ching) family (Mother & Father, Son & Daughter) : check

Former Driver : N/A

Former Housekeeper : check

Housekeeper's husband : check (plus loan shark excuse may as well be made up)

Normal family (Husband, Wife, Daughter, Son) : not impossible

The one and only objective condition to be fulfilled is an income from which everybody can leech.

We're to assume the inhabitants of the house (Park family) are legit, but AFAIR we get close to no background on them. The only approximation of it is a wall with a few framed pictures of the perfect family, a framed ad/article about Nathan [sic, the parasite son is dubbed Kevin] Park the High Tech golden boy, and a framed obscure diploma [resic, these are unforgeable right ?]. Wouldn't it be possible, for example, that the present occupiers of the house used the same kind of tricks to blackmail the former ones out of the picture ? To me, it would fit well with the spirit of the movie, survival of the fittest parasite; by being at the top of the pecking order, they get to employ other parasites to do their menial work.

But the main reason I'm not discarding the hypothesis revolves around the character of the rich woman. Almost all the time she is a very dumb, very easily manipulated, very weak, very unreliable. Is she really, or is she playing the part just like the others are ? The only scene where she and her husband think they're alone, they immediately sound and act in a more complex manner. Am I underestimating the weight of social norms on people's behaviour in public, especially in South Korea.

There are probably many points to be made against this understanding : if they were so bright and cunning, they wouldn't have had problems with their hyperactive kid (or ...). They might also have cooperated with one another to reach a symbiotic parasitic life instead of destroying the whole organism; by the way, to me the dramatic turns of events near the end felt quite odd, if not anticlimatic : as they seemed to be somehow enjoying themselves as much as they were making ends meet, I'm not convinced with their total loss of cold blooded control with the Housekeeper and Husband. And the mood neither was as unequivocally tragic as in, for instance, A Requiem For A Dream, nor was the pulp violence as parodically exagerated as in most Tarrantino movie.

Finally, a small disgression about the Normalcy Vs. Deviancy showcase. Though it was done in a very different way, it made me think of Captain America, inasmuch as the persons or groups supposed to be pariahs, unlawful, lazy turn out to be a lot more intelligent, honnest, cheerful, connected and able than postcard normal people.