Interpersonal theory was developed by American psychiatrist Harry Sullivan. It is a theory of personality development emphasizing coping and defensive mechanisms. Sullivan argued that personality is formed as a person's ego interacts with others. He believed that personality was the result of the ego's attempt to assert and defend itself against threats or attacks by others.

According to Sullivan, both positive and negative aspects of personality derive from the innate desire to protect one's sense of self. A famous entertainer like Prince develops charisma, for example, in order to assert his worth and position within his social circle. He recieves positive reinforcement in the form of approval and friendship.

Sullivan argued that negative traits stem from a person's desire to disassociate with parts of their experience that threaten their ego. A famous musician may develop addictive tendencies as a means of coping with his lack of confidence in his ability.