Final answer:
Sigmund Freud was a pivotal figure in psychology who introduced the concept that psychopathology is multiply determined, focusing on the role of the unconscious mind and its influence on behavior.
Step-by-step explanation:
The most notable early adherent to the idea that psychopathology is multiply determined was Sigmund Freud. Freud's development of psychoanalytic theory significantly impacted the field of psychology. He theorized that the unconscious mind played an important role in an individual's behavior and introduced the concepts of the id, ego, and superego as the main components of personality. Freud also proposed that personality develops through a series of psychosexual stages, and that unresolved conflicts in these stages could lead to psychopathology. His ideas about the unconscious mind and its influence on conscious behavior laid the groundwork for understanding that psychopathology can stem from various unconscious psychological processes.