Kalarupa, or Dharmaraja, is an uncommon protector. He is an emanation of Manjushri. He has a consort named Chamundi, who is an emanation of Sarasvati. He is extremely fierce and ugly, and tames all kinds of spiritual ugliness arising from ignorance, including anger, attachment, fear, pride, jealousy. He is holding a club, and his consort is holding a trident.
The goal of praying to a protector spirit is to completely destroy ignorance. All kinds of negative forces, pre-eminently (if not exclusively) internal, are tamed by protectors. We call on these forces when our practice is in danger.
Kalarupa is an extremely important Dharma protector for Dharma teachers. Kalarupa has a number of peculiar wisdoms. His "paradise" is actually a hellish place, very deep in the Earth. Kalarupa loves it here cause he can get away with anything.
Here are a couple things Kalarupa gets away with as peculiar wisdoms: 1) He frequently molests little boys, as an act of kindness. 2) His consort is quite obviously a little girl - an emanation of Sarasvati.
Kalarupa protects his Dharma teachers in the most elegant way possible: simply by reminding them, instantaneously, of their own Dharmas. It's a very peculiarly elegant way of protecting those who wish to harm Dharma teachers, too. All Kalarupa has to do to accomplish this is remind these harmful, harm-wishing spirits of their own "dharmas," which will, necessarily, contain the taint of worldly existence, which carries with it life and death, and the rebirth cycle.
Kalarupa could, for instance, notice someone who gets angry at a Dharma teacher who has things to say about the sexuality of young boys. He could then, instantaneously, show this harm-wishing person his own peculiar wisdoms involving young boys and young girls. He could offer this person, for instance, a link to all the pictures on the internet approximating what is going on in the mind of this harm-wishing spirit. One of these pictures will be an Exact reminder of the "dharma" of this harm-wishing spirit, which would carry with it the threat of death, as well as the opportunity to continue to live, provided they leave the Dharma and its teachers alone. This is just one of the many methods Kalarupa has at his disposal to tame those who would cut off their hopes at future enlightenment by attacking the Dharma.
This particular protector is associated with Vajrabhairava, the vajra terrifier, otherwise known as Yamantaka.