Heruka [Tibetan: Wylie: 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 East Asia, these are called Wisdom Kings.
Herukas represent the embodiment of indivisible bliss and emptiness. They appear as Iṣṭha-devatā [Tibetan: Wylie: yi dam] or meditational deities for tantric sādhanā, usually placed in a mandala and often appearing in Yab-Yum.
Heruka represents wrathful imagery with indivisible emptiness [śūnyatā], bliss, peace, wisdom, compassion [bodhicitta], and love. Herukas represent unified consciousness, with emptiness being a reflection of "non-phenomena" or emptiness which is "all love," or removal of imagery to reach universal love, mercy, and compassion-mind.
The Sanskrit term Heruka was translated into both Chinese and Tibetan as "blood drinker," which scholar Ronald Davidson calls "curious," speculating that the nonliteral translation derived from an association the term has with cremation grounds and 'charnel grounds' [Sanskrit: śmāśāna] [which absorb the blood of the dead]. Sanskrit terms for blood drinker include asrikpa, reflecting a Sanskrit word for blood [asrik], and raktapa, raktapayin, or rakshasa, derived from an alternate root term for blood [rakta]. Unlike the Chinese and Tibetan [Tratung, wylie: khrag 'thung] terms used to translate it, the Sanskrit term heruka does not literally mean blood drinker, although the fact that it was rendered as such into two other languages strongly suggests an according Indian interpretive etymology.