Black bile is one of the four humors in ancient and medieval medicine, believed to be produced by the spleen. It was thought to be associated with melancholy and sadness. The concept of black bile originated from the teachings of Hippocrates and was later expanded by Galen, who linked it to various physical and emotional conditions. In the humoral theory, an imbalance of black bile was thought to lead to illness. Treatments often aimed to restore balance among the four humors: black bile, yellow bile, blood, and phlegm. This theory has since been replaced by modern medical understanding, but it played a significant role in the history of medicine.