Final answer:
The ancient Greeks believed that four different personality types were strongly related to bodily fluids. This idea, based on the four humors, was first proposed by Hippocrates and later expanded by Galen.
Step-by-step explanation:
The ancient Greeks suggested that there was a strong relationship between four different personality types and bodily fluids. Hippocrates, around 370 BCE, theorized that personality traits and human behaviors are based on four separate temperaments associated with four fluids or "humors" of the body: choleric temperament (yellow bile from the liver), melancholic temperament (black bile from the kidneys), sanguine temperament (red blood from the heart), and phlegmatic temperament (white phlegm from the lungs). Later, Galen expanded on this theory, suggesting that diseases and personality differences could be explained by imbalances in the humors, with each person exhibiting one of the four temperaments, which could be identified as passionate and bold, reserved and anxious, joyful and eager, or calm and reliable.