German-British psychologist, one of the leaders of the biological field and one of the most cited authors in the history of applied psychology, the author of the popular intelligence test (see Eysenck-Gorbov Intelligence Tests in Section 1.7. Key Psychological Concepts in Personality Psychology) and a number of questionnaires and psychodiagnostic methods. Many of the scientist’s works are based on the assumption that the entire set of traits describing a person can be represented by two main factors: extraversion/introversion (orientation of the personality either to the world of external objects or to the subjective inner world) and neuroticism (emotional stability or instability). The intersection of these two bipolar characteristics allows us to get a curious result – a fairly clear attribution of a person to one of the four types of temperament: choleric, sanguine, phlegmatic, melancholic.