The terrible face of Yama, who represents death, peers over the top of the Wheel. In spite of his appearance, Yama is not evil. He is a wrathful dharmapala, a creature devoted to protecting Buddhism and Buddhists. Although we may be frightened of death, it is not evil; just inevitable.
In legend, Yama was a holy man who believed he would realize enlightenment if he meditated in a cave for 50 years. In the 11th month of the 49th year, robbers entered the cave with a stolen bull and cut off the bull's head. When they realized the holy man had seen them, the robbers cut off his head also.
But the holy man put on the bull's head and assumed the terrible form of Yama. He killed the robbers, drank their blood, and threatened all of Tibet. He could not be stopped until Manjushri, Bodhisattva of Wisdom, manifested as the even more terrible dharmapala Yamantaka and defeated Yama. Yama then became a protector of Buddhism.