Cattell refers to Raymond Cattell, a prominent psychologist known for his work in personality theory and psychometrics. He developed the 16 Personality Factor Questionnaire (16PF), which assesses various personality traits. Cattell's research emphasized the importance of both surface traits and source traits in understanding human behavior. In addition to his work on personality, Cattell contributed to the field of intelligence testing. He proposed the distinction between fluid intelligence and crystallized intelligence, which describes the difference between problem-solving abilities and knowledge acquired through experience. His theories have influenced both psychology and education.