Light but interesting reading....
Over the last 25 years, psychologists have found that personalities coalesce around five basic traits, dubbed the Big Five. Everyone can be described as having varying levels of agreeableness, conscientiousness, neuroticism, extroversion and openness to experience.
Contrary to common perception, people aren't confined to certain personality types. Usually, no one is entirely an extrovert or an introvert, or a total neat freak or a slob. While a minority may be at the extreme ends of a trait, most people are somewhere in the middle.
Animals have personalities also but we might not think of that often. I did not think about wild animals having different personalities.
An evolutionary root of personality means traits must be inherited. So whether you'd like to admit it or not, much of your personality comes from your parents. In fact, for humans, about half of the differences in personality are genetic, Soto said. The rest of the variability in personality comes from your environment, such as life experiences and birth order. (First-borns tend to be more assertive, while second-borns tend to be funnier; younger siblings use humor to diffuse the power that older ones have over them, Sulloway explained.)
We can, to some extent adjust our personality to the circumstance. We have evolved to learn from our environment.
As we age our personalities tend to change as well. We might even be able to adjust our personalities on purpose.
So while personality may make you who you are, it won't necessarily make who you will be.