Shiva is known by various names like Mahadeva and Shambhu.There is another term used for Shiva that is Mahakala. I would like to know if Mahakala is only a name for Shiva or another form of Him. Also if it is just another name what is the reason behind calling Shiva Mahakala?
In the city Avanti, according to Shiva Purana, 4 brahmins were worshipping Shiva Linga.
A king of the Daityas called Dūṣaṇa, arrogant with boons obtained from Brahma, he stopped performing of Vedic rites in the shrines and holy centres . On coming to know of the intent of the Daityas, the brahmins were not at all distressed because they were engaged in meditating on Śiva.
They sat firmly engaged in meditation. On seeing them thus the mighty Dūṣāṇa shouted “Let them be killed. Let them be bound.” But the brahmins, engrossed in meditation on Śiva did not hear the shouts.
When the wicked Daitya desired to kill the brahmins, the spot near the Pārthiva idol caved in with a loud report.,
From the chasm thus created, Śiva rose up assuming a hideous form. He became famous as Mahākāla, the slayer of the wicked and the goal of the good.
“I am Mahākāla (the great god of death) risen up against the wicked like you. O sinful one, go away, leave the presence of these brahmins.”
After saying this Śiva reduced Dūṣaṇa and his army, to ashes immediately with a mere sound of Hum.
Mahakala is a form of shiva that consumes all things during the dissolution of the universe.it is his highest form and the Veda have a whole hymn to his mahākāla form in the form of kāla. http://www.mahapashupatastra.com/2014/11/the-unfading-glory-of-mahakala.html
mahāKāli consumes mahākAla but he does not cease to exist,rather they both become As Brahmarūpā Kālī.As per Rudrayāmala Tańtra, Brahmarūpā Kālī eternally remains in Her four-armed form after contracting Śiva and Śakti within Herself, residing in the cosmic Mahāśmaśāna.