The image above (from Bokar Monastery in Mirik, India) depicts the wrathful form of Kālacakra, known as Vajravega (rdo rje shugs). This deity features in the main Kālacakra meditation practice in two areas: the protective sphere meditation near the beginning of such practices, and then during the main generation process of Kālacakra he radiates out from the commitment-being to attract the awareness-beings. The painting to the left shows Vajravega surrounded by the 60 protectors of the protective sphere.
In many ways, Vajravega is similar to Kālacakra. He is black, rather than blue, in colour; he has four faces of the same four colours, but each face is angry and baring the teeth instead of having different expressions. He also has a red right leg and white left leg. As with Kālacakra, he has 24 main hands, holding the same implements as Kālacakra, although these are in wrathful forms where relevant. In addition he has two extra hands; these can clearly be seen above his main white hands in the image. The right one is black and holds the head of a demon, the left is yellow, pointing, and holds a skull of blood; they both hold an elephant skin over his back. He wears ornaments either of vajras or bone, and also of snakes (nāgas).
Vajravega is introduced in the Kālacakra Tantra and its commentary, the Vimalaprabhā, in one of the preliminaries to the main Kālacakra empowerment. A vajra-protective sphere containing Vajravega and the 60 protectors is established to protect the surrounding area and the site where the empowerment will take place. The same process is followed for the main Kālacakra sādhana. See below for a description of this protective sphere.
Towards the end of the fourth chapter of the Vimalaprabhā there is a description of a deity that is identical to Vajravega, except that he is in union with a consort, Viśvamātā. This deity is not named, and is simply called "One holding the fresh elephant skin". He usually goes by the name of Mahāsaṃvara Kālacakra (dus 'khor sdom pa chen po). He is identical in every respect to Vajravega. His consort has one face and two hands, holding a curved knife and human skull of blood. She is yellow in colour and naked, with her hair hanging free.
A couple of pages later in the Vimalaprabhā there is a description of a short practice for the meditation of Vajravega – this time without a consort, and surrounded by eight Nāgas. The text does seem to be treating these two as separate deities, even though the male deities are identical. Some writers, such as Mipham. consider Mahāsaṃvara and Vajravega to be identical, while others, such as Tāranātha, consider them to be distinct.
Perhaps the best way to consider them is that Vajravega, without the consort, is the protector aspect, and Mahāsaṃvara is the yidam. The image to the right of Mahāsaṃvara is linked in from the Rubin Museum of Art website – click on the image to visit that site in order to view it in greater detail. (The colour green of the consort is presumably the result of changes in the pigmentation – she should of course be yellow.)
Being a yidam, Mahāsaṃvara is naturally associated with a maṇḍala, in which the deity is imagined during the meditation practices. This maṇḍala is very unusual, in that it is circular. It also has eight doorways. This practice is preserved in both the Sakya and Jonang traditions, and the relative dimensions of the maṇḍala in those traditions are somewhat different, although both are circular with eight doorways. For a description and illustrations of the maṇḍala of Mahāsaṃvara see this page.
Vajravega's protective sphere:
The sphere exists in a vast dharmodaya – in shape like an upside-down pyramid – open at the top. It is not specified, but as the dharmodaya is green, it clearly represents the element of space, and Banda Gelek states that it is in the empty realm of the whole of the animate and inanimate worlds. (Click on any of these images to see a higher resolution version.)
The other four elements – of earth, water, fire and wind – form together to create the protective sphere inside the dharmodaya. The base, or ground, is hemispherical in shape and is said to cover (and thereby protect) the region in which the practitioner is performing the ritual; this is said to be a space large enough to contain 100,000 villages, or, have a diameter of 24 yojana (dpag tshad). The surface of the ground is said to be flat like a mirror. Around the edge of the ground are five tall concentric vajra-walls. Their tops lean in slightly. Their colours are the same as those of the walls of the body and speech palaces of the main Kālacakra maṇḍala. Here, they are shown in the same order as with the maṇḍala – from the inside: green, black, red, white and yellow. This is for peaceful purposes, such as protection. Their order is reversed for wrathful practices such as striking phurpas. Above is a vajra-canopy (or, tent). This either sits on top of the walls, or just outside of them, the effect being that the whole appears as a complete sphere. These are called the outer walls and canopy.
Next, are the inner walls and tent. In the centre of the flat ground is a circular house with eight doorways (this is very reminiscent of the maṇḍala palace of Mahāsaṃvara Kālacakra). This is similar in form to the main ground, but half its size. Around its perimeter are three concentric vajra-walls, also leaning in slightly. Their colours are the same as the three walls of the mind palace of the Kālacakra maṇḍala – black, red and white, from the inside. This is considered to cover the area up to the horizon of the place where the ritual is being performed (considered by some to be an area of diameter 12 yojana). The walls also have above them a matching vajra-canopy, also forming a complete sphere.
Then, in the middle of the surface inside the triple inner walls is another circular house, the same as before, but half its size and without either circling walls or canopy. In the middle of the flat upper surface of this structure is a three-storied house, the essence of body, speech and mind. It is said to be 200 cubits in width (or diameter – some consider it to be circular in shape) with each storey 100 cubits tall. The roof structure on the top is also 100 cubits, and so the overall height is 400 cubits. The building is either the colours of the directions (as shown here) or all green.
Finally, inside the three-storied house is a ten-spoked vajra-sphere, inside of which is the lotus and sun on which stands Vajravega. This sphere is also the colours of the directions, with hollow upper and lower spokes and flat spokes in the cardinal and intermediate directions, in the shape of swords. The hub of the sphere is in the middle of the middle storey; the upper and lower hollow spokes are fixed into brackets in the ceiling of the upper storey and the floor of the lower storey; they pass through holes in the two other ceilings that are in diameter about one third the width of the building. The sixty protectors are arranged in the upper and lower spokes, on the surfaces of the flat spokes, and in various places between or inside the outer and inner sets of walls.