Answer: Carl Gustav Jung
Explanation: Jung was a psychologist, he used the term "inward turn of libido" and "an outward turn of libido" these terms soon became introvert and extrovert.
"Carl Jung proposed core ideas in his exploration of personality, including the constructs of introversion and extroversion.
Jung (1921) suggested the principal distinction between personalities is the source and direction of an individual’s expression of energy – defining extroversion as “an outward turning of libido” (para.710) and introversion as “an inward turning of libido” (para. 769).
The interest of the introvert is directed inwards; they think, feel, and act in ways that suggest the subject is the prime motivating factor. Extroverts, on the other hand, direct their interest outwards to their surrounding environment; they think, feel, and act in relation to external factors rather than the subjective."
From - Positive Psychology
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