Personality is defined as the inner psychological characteristics that determine how a person responds to their environment. It includes specific qualities, attributes, and factors. Personality can change over time or due to major life events. There are several theories of personality, including Freudian theory which focuses on unconscious drives, trait theory which views personality as a set of traits, and self-image theory which ties personality to how people see themselves. Marketers study personality to understand consumer behavior and how brands can develop personalities to appeal to different types of consumers.