In the Tantra, it’s said that when Buddha Shakyamuni meditated under the bodhi tree, great power and wisdom arose in his mind right before attaining enlightenment. This manifested to defeat and overcome the immense hindrances and negative forces. The Mahakala is that power and wisdom. Similarly, the power and wisdom that Guru Rinpoche manifested to tame all the evil forces in Samye is also the Mahakala.
Characteristically black or deep blue.
Four-Armed Mahākāla
(San; “great black one”): A dharmapala predicted by the Buddha, Four-Armed Mahākāla is a particular protector of the madhyamaka teachings and of the Chakrasamvara tantra. He is a manifestation of Heruka Chakrasamvara. He was also a special protector of Surmang. His symbolism is based on vajra anger and compassion.
As described in The Myth of Freedom, his four arms represent the four karmas:
One left arm holds a skull cup of amrita, the intoxicating nectar of the gods, which is a means of pacifying.
One right arm holds a hooked knife, a symbol of enriching.
The second right arm holds a sword, which is a way of magnetizing or gathering together energies. The sword need not strike; just by its being waved, the energies are rallied.
The remaining left arm holds the khaṭvāṅga (trident) which destroys or subdues. Its three prongs cut through the root kleshas of passion, aggression, and ignorance with one thrust.