He may be the emissary of Vāsava, or of Vaiśravaņa; or he may have been sent by Rāma himself from eagerness to get at the whereabouts of Sita.
वासवस्य भवेद् दूतो वैश्रवणस्य वा। प्रेषितो वापि रामेण सीतान्वेषणकाझ्या॥