Gordon Allport: Identified personality traits and believed these traits were innate.
Raymond Cattell: Defined two types of traits, surface traits and source traits. He identified 16 source traits.
The Five-Factor Model (Big Five)
Openness: A person's willingness to try new things and be open to new experiences
Conscientiousness: A person's organization and motivation, e. g. being on time, careful with belongings.
Extraversion: two personality types: extraverts and introverts
Agreeableness: emotional style of a person
Neuroticism: emotional instability or stability
Below are suggested books from the library that focus on Trait Theory that may be useful for your research project.