Great question, first of all!
Personality comes from many different combinations.
First, genes could have something to do with it.That specific set of genes survived by acting a particular way (intelligent, daredevil, witty, etc.).
Second, culture. Third, how the individual was treated. Fourth, how the person reacts to the world around him or her. Fifth, circumstances the person experienced as a child, young adult, etc.
It's a combination of genetics and their own life experiences.
Their hearts and minds.
It's mostly sociological. Combination of family, friends, background, culture, and societal influence. It's much more complicated than can be easily explained in a few short sentences.
The proteins in your DNA
the 5 th person down their family trreee
Response to environment and related stress factors.