Q is the young boy who is part of Q team. He doesn’t remember who he is and doesn’t appear to remember how he got the helmet on his head. During the game you will discover that there is a small panel on the side of the helmet that allows for the input of a code. This code is found during the ending where Q meets Zero in the quantum computer room. The code is given to you directly, so there is no way to miss it so long as you are paying attention.
If you have forgotten the password or are too impatient to wait for it, then here is the password for Qs helmet.