In my game, when I instantiate a particular prefab, I need to show a GUI window, then let player do some actions, finally close that window and update the caller `GameObject` with the info inserted from user. 

So my question is: how to save the reference of the `GameObject` caller to update it at the end of the user action. 

Consider that I call some sub functions and I don't want to pass a `GameObject` through all functions. 

Is there a way to save a gameObject reference in a global variable ? I'm using a static class for that purpose.