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Khar was a cursed being by Shiv Jee and he would be released from his curse by Raam of Dasharath. In the Shesh Dharm of Mahaa Bhaarat in the discourse between Bheeshm Pitaamaha and Yudhishthir, it is said that sage Yagyavalkya Jee had three sons - Chandrakaant, Mahaamedhaa and Vijaya. These three Brahmin became Khar, Dooshan, and Trishiraa by the curse of Shiv Jee. 

The first one Chandrakaant is Khar. And the disciples of the three Brahmin scholars were fourteen and they also became Brahm Raakshas, who are being sent now. On listening Shoorpankhaa, Khar came to know that Vishnu is in the form of Raam and thus Khar wanted to get release from his curse by Raam, and hence firstly he sends the fourteen Raakshas, who were their 14 disciples, and later these three brother also follow them and thus get released from their Shaap.

[Taken from Valmiki Ramayan 3/19]