The idea that there is a part of the mind that is not directly accessible to awareness but still drives a person's thinking and behavior is most directly attributable to

Freud

Explanation:

Sigmund Freud was the father of psychoanalysis. Psychoanalysis was the method to bring out the emotions felt from the unconscious mind to the conscious mind. This phenomenon is being used to treat the mental illness of a person. This is a theory that explains the behavior of a person. Freud proposed a personality theory that explains our childhood events that influence our behavior in adulthood. These experiences shaped the personality of a person. For instance, anxiety is a behavior that occurred due to our unconscious feelings or fear in the childhood period.

Sigmund Freud

Explanation:

The answer is Sigmund Freud.

Sigmund Freud, most popularly known as Freud was an Austrian neurologist. He is known as the father of psychoanalysis.

Sigmund Freud highlighted the importance of the unconscious mind and argued that people are not aware of the unconscious mind but it drives a person's behavior and thinking. According to him, the unconscious mind influences the behavior and the thinking capabilities of an individual to a great extend.

Thus the answer is - - Sigmund Freud.