Roberto has a sanguine temperament because he would be described as enthusiastic, active, and social. Temperament theory has its roots in the ancient four humors theory. It may have origins in ancient Egypt or Mesopotamia, but it was the Greek physician Hippocrates (460–370 BC) who developed it into a medical theory. He believed certain human moods, emotions and behaviors were caused by an excess or lack of body fluids (called "humors"): blood, yellow bile, black bile, and phlegm.