The belief in a direct correlation between the stars and human character which dates back to the Hellenistic era was enormously popular in the Islamic world, due principally to the writings of Albumasar. This theory argues that each planet and each kind of human temperament is typified by two of four qualities (hot, cold, dry, moist) and dominated by one of the four elements (earth, water, air, fire). Jupiter, moist and hot, is dominated by air and governs the sanguine humour of a typically balanced, extroverted and free-spirited person. Saturn, dry and cold, is dominated by earth and governs the melancholic humour which prompts introversion. Mars, hot and dry, is dominated by fire and governs the choleric humour with its fiery qualities. And the Moon, cold and moist, is dominated by water and governs the phlegmatic humour.