Final answer:
Humanistic psychologists Abraham Maslow and Carl Rogers believe in free will and the drive towards self-actualization as central to mental development.
Step-by-step explanation:
The theorists who believe that people have free will and that the natural direction of mental development is towards growth and achieving potential are humanistic psychologists, Abraham Maslow and Carl Rogers.
They posited that individuals have a fundamental drive to become self-actualized, to fulfill their highest potential. Maslow's hierarchy of needs is a well-known construct within his theory, wherein the pinnacle need is self-actualization or the realization of one's full potential.
Furthermore, Rogers and Maslow both emphasized the intrinsic capacity for self-improvement and personal growth, contrasting with deterministic views such as those presented in psychoanalytical or behavioral theories.