Mahakala is the most importan terrific protector of Tibetan Buddism. He is the wind!
He is black and six-armed. Though fierce in his trampling upon the evil spirits of delusion and greed, he is actually consindered to be the agent of Avalokiteshvara or Chenrezig, the angelic Bodhisattva of great compassion. Mahakala is frightening in appearance, because his responsibility is to protect all beings from evil.
Mahakala is typically black in color. Just as all colors are absorbed and dissolved into black, all names and forms are said to melt into those of Mahakala, symbolizing his all-embracing, comprehensive nature. Black can also represent the total absence of color, and again in this case it signifies the nature of Mahakala as ultimate or absolute reality. This principle is known in Sanskrit as "nirguna", beyond all quality and form, and it is typified by both interpretations.