Who is credited with the belief in four body humors and their association with different personalities?

The belief in the four body humors—blood, phlegm, yellow bile, and black bile—along with their association with different personality types is primarily attributed to Hippocrates, often regarded as the "Father of Medicine." Hippocrates posited that an imbalance of these humors could result in both physical illness and emotional disturbances, leading to different personality traits. For example, he theorized that an excess of blood could produce a sanguine personality, characterized by sociability and warmth, while an excess of black bile might lead to a melancholic disposition, marked by introspection and sadness.

While Galen, who came after Hippocrates, expanded upon these ideas and integrated humor theory with his own medical practices, the original conceptualization links back to Hippocrates. Aristotle's ideas on personality and psychology were different, focusing more on the soul and its functions rather than the humors. Freud's theories of personality were rooted in psychosexual development and the unconscious, significantly diverging from the earlier humorism theory. Thus, Hippocrates is recognized for laying the groundwork that connected the physical state of the body with psychological attributes through the humoral theory.