Explain in detail how galen, a physician during the middle ages, expanded on hippocrates’ theory of the four humors and explain what he believed each humor represented. (site 1)

Hippocrates believed that there are four humors in human body which need balance for a healthy being. These were:
Blood, phlegm, yellow bile, and black bile.
Galen expanded the idea of the humors and introduced four temperaments which were these:
choleric (hot / dry), melancholic (cold / dry), sanguine (warm / moist), and phlegmatic (cold / moist).
Another expansion Galen did was that he gave each humor/temperament physical and psychological qualities and said that even the food items have an association with the certain humor, those foods can effect certain humor in certain ways.