Who you are is not determined by you. God has made you who you are, at least in all the ways that do and ever will matter. The ways that matter most are that you are fearfully and wonderfully made by God(Psalm 139:14), and you have a calling and a purpose He laid out for you, and placed in you something that no one else has/can do. Those are the greatest and most important things about you.
Who you are is not defined by Satan. He may in fact know who you are better than you do, and he is doing everything he can to keep you from knowing who you really are. He is a liar who makes his full-time job to convince you that you are something you really aren't, and to convince you that you aren't things that you really are. His best revenge against Christ is to steal you from Him.
Who you are is defined by God.
Before I go on, may I clarify something. Sin does not define you. A sinful nature and flesh does not define you. That is why homosexuals and murderers are not sin in themselves, they are sinful. We were all created to serve God in a perfect and holy way, and because Adam fell, we are flawed and impure. God has defeated death through Jesus' death and resurrection, and that same power is available to you. If two things are in you, and one is greater than the other, then surely it must define you (or at least who you're supposed to be).
So, the closer you get to who God originally made you to be, the more of your real self you are.
Who you really are is defined by God (whether you realize it or not). What you do with who you are is up to you. You can be fooled, decieved, ignorant, or know it and be foolish. God either has or so badly wants to call you to something so much greater than these.
Back to the painter analogy. God painted you exactly how he wanted you to be, then sin came and smeared that paint. Now, you as the painting must choose to either let Him fix you by seeking and believing in Him, or choose to be "jacked up." If you're truly seeking God, no devil will be able to hold you back. God will reveal the details of you as a painting, and sin and death are helpless against His power.