Learn English – Single word request for someone with hidden but good intentions that seem opposite to their appearance

I am looking for the word that describes someone that does something for a hidden or secretive reason that is hard for others to understand because that person wouldn't seem like the type to do such a thing.

An example could be a very childish person going to a party and others think that just wanted to go to have a good time, however that person secretly has a much more important role that is seemingly very sophisticated and well thought out. This intention or motive is hard for others to pick up on.

I guess another example could be a character in a game or tv show that seems very nice on the outside but has a hidden ulterior motive that it seemingly can be both beneficial but disliked by the one who is in the dark.

It is like the person is concealing this hidden trait for the benefit of others.