Personality is another one of those psychological concepts that has made its way into the popular vernacular, lending itself to misinterpretation and misunderstanding. This is such a complex topic that many of the major schools of psychological thought have their own take on the subject. Thus begins another "series" of sorts. This time I will try to clarify some issues on and present some theories about personality, or what makes you YOU. Let's begin with a basic definition.
Personality: the unique and relatively stable ways in which people think, feel, and behave. In its most general terms, you are a combination of your way of thinking, your general emotionality, and the choices you tend to make. This also includes the situations that lead to your greatest comfort and your preferences, even in the face of behaviors in which you would rather not engage but still sometimes feel compelled to given certain circumstances. Personality is often confused with one's character.
Character: value judgments of a person's moral and ethical behavior. Your character is the judgment that others (and sometimes yourself) lay at your feet based on the observable data that you present to them. Note that character does not include your actual motivations or emotions concerning the matter, only the behaviors that others can see. This is due to the fact that the vast majority of humans (around 99.998%) are NOT psychic and cannot actually see into another person's soul or mind or heart. We infer people's motivations based on circumstantial evidence, but our character judgments are still flawed by the fact that we cannot know ALL of the relevant information involved that may or may not have had an impact on the resulting behavior of another. As my mother says, we judge others by how we live our lives. All subsequent character judgments are biased by our own personal lenses formed from our past experiences. Plus, character is based upon the behaviors that another person chooses to show others.
Temperament: the enduring characteristics with which each person is born. Temperament is really the baseline emotionality of an individual. This inherited part of personality, which is exhibited as early as day 1 of infancy, is simply a baseline upon which we build the rest of our personality--the cognition and behavior. Infants can generally be classified into one of four temperaments--easy, slow to warm up, difficult, or undifferentiated. The easy children tend to be generally happy babies who adapt to change and new environments readily. If upset, it doesn't take much to placate them. The slow to warm up babies tend to take their time in building their comfort zone. When in the comfort zone they are satisfied. Removing this infant from their comfort zone (changing routine, introducing something new) will significantly distress them, however, they will eventually adapt over time, so long as changes are introduced slowly and one at a time. The difficult baby seems to have his/her mind set from the get-go and is not willing to budge for anything. So long as the routine and the environment stay the same, they will be content. Any change will be met with extreme resistance and will very rarely be accepted. They do not like change at all. The rest of the children are born with an undifferentiated temperament. This means that they have not made up their mind yet as to how they will deal with change or new situations. Sometimes these infants exhibit characteristics of more than one temperament, sometimes they just don't have any clearly distinctive characteristics (of the aforementioned three types) until later in their infancy or childhood.
So, the bottom line is that, in a nutshell, your personality is what you do, how you feel, and your thought processes that make you unique. True, there are overlaps between individuals, yet there is no exact copy of the unique combination of all the components that make a person who they are. One of the reasons personality is so debatable from a theoretical perspective is the fact that we show different "faces" to different people we encounter. We never show every single nook and cranny of our entire being to any one person. We always keep something--sometimes a large part, sometimes only a tiny spark--in reserve for just ourselves. And there is even a part of our personality that we have not uncovered yet. Some theorists (Maslow, Rogers, Erikson to name a few) believe that we are constantly discovering new things about our own personalities as we encounter new life experiences, so we may never find everything there is to know about our self.