Dhenuka (धेनुक) also known as Dhenukasura, is a donkey demon killed by Balarama, the elder brother of Krishna.
Killing of Demon Dhenukasura in Talavana
Bhagavata Purana Skanda 10 chapter 15 , states that Dhenuka, ruled over a forest of tala or palms trees, situated on the banks of the Yamuna River. Once Balarama, Krishna and cowherds wandered into this forest, attracted by the fragrance of the fruits of the palm trees.
फलानि तत्र भूरीणि पतन्ति पतितानि च ।
सन्ति किन्त्ववरुद्धानि धेनुकेन दुरात्मना ॥
In that Talavana forest many fruits are falling from the trees, and many are already lying on the ground. But all the fruits are being guarded by the demon Dhenuka (धेनुक).
When Krishna commented on the possible sweet taste of the fruit, Balarama shook the trees and the fruits fell on the ground. Dhenuka knowing the same charged at Balarama and kicked with his hind legs. Balarama caught hold of Dhenuka’s legs and whirled him towards a tree, shattering his chest, neck and waist as the tree fell with the demon. Balarama killed Dhenuka demon and set the forest open for the cowherds.