Thought provoking philosophical questions.

Who are you? What defines who I am as a person? Am I just a summed total of my behaviors loosely identified as some kind of personality? If that's so, then who you are is just a chemical processor which causes these behaviors in response to your animalistic needs. You might be an angry person due to your heighten sense of fear, which dates back to the days we lived in a more hostile environment. You might be a bit of a joker but then a again this need to make others laugh could be related to your desire for dominance or to release aggressive tension.
Every human behavior has a root cause based on our requirements as biological beings. When you add these up, they account for most of what we call a personality. But we know that these behaviors can be changed. We know chemicals can be introduced to a human being to make them act entirely the opposite way permanently or temporarily. So if the human personality can be so fundamentally altered, does the idea of you even exist at all?