The author of 'The Interpretation of Dreams' is Sigmund Freud, a five-letter word spelled 'FREUD'. Freud was an Austrian neurologist and the founder of psychoanalysis, a clinical method for treating psychopathology through dialogue between a patient and a psychoanalyst. He is best known for his theories of the unconscious mind and the defense mechanism of repression. His book 'The Interpretation of Dreams' is considered one of the most influential works of psychology in the 20th century.