Theorists
Gordon Allport
Raymond Cattell
Hans Eysenck
 

Traits
Openness to Experience
Conscientiousness
Extroversion
Agreeableness
Neuroticism

Links criticizing Trait Theory
McAdams
Mischel
 

The five-factor model is comprised of five personality dimensions (OCEAN): Openness to Experience, Conscientiousness, Extroversion, Agreeableness, and Neuroticism.      

The earliest form of Trait Theory is traced back to Ancient Greece at the time of the famous physician Galen.  Galen thought our personality was a reflection of the four humors (fluids) that make up our bodies. 

Yellow bile - bad temper, irritability (Choleric)

Black bile - gloomy, pessimistic (Melancholic

Phlegm - Sluggish, non-excitable (Phlegmatic)

Blood - Cheerful, passionate (Sanguine)

The kind of strict characterization suggested by theorists just as Galen's suggests there are very different types of personalities.  In more recent years personality theories have leaned more towards the notion that we all have similar personality traits but we differ in terms of the extent to which we exhibit that trait.

A trait is considered to be a stable, cross situational individual difference.  Currently the most popular approach among psychologist for studying personality traits is the five-factor model or Big Five dimensions of personality.  The five factors were derived from factor analyses of a large number of self and peer reports on personality-relevant adjectives and questionnaire items.