When राम and लक्ष्मण were staying in पञ्चवटी a demoness named शूर्पणखा made approaches to them and लक्ष्मण cut off her limbs and sent her away. Then a राक्षस army came under the leadership of खर , दूषण and त्रिशिरस् and पृथुग्रीव was one of the twelve prominent soldiers of that army.

(Sarga 26, Araṇya Kāṇḍa Vālmīki Rāmāyaṇa)