Heruka (Sanskrit; Tib.khrag 'thung), is the name of a category of wrathful deities, enlightened beings in Vajrayana Buddhism that adopt a fierce countenance to benefit sentient beings. In China and Japan, it was named as Wisdom King. Herukas represent the embodiment of indivisible bliss and emptiness. They appear as yidam or meditational deities in tantric sadhana, usually placed in a mandala and often accompanied by a yab-yum consort.
Read more about Heruka: Derivation and Meaning of The Term, Eight Herukas of The Nyingma Mahayoga