This unnamed Prophet was a San Shyuum (Prophet) of the Covenant Empire responsible for supply routes in an unknown sector of the Milky Way Galaxy and served as the primary antagonist of Halo Legends episode: The Babysitter.
Prior to the visit of Heian, a planet under Covenant control, a covert human team: consisted of three ODSTs (Orbital Drop Shock Troopers) led by SPARTAN II Cal-141, managed to slip pass Covenant Army patrols and take up an overwatch position above a landing zone in a staging area. Just before the Prophet was about to be shot, a Brute Chieftain snuck up on the team and injured Cal, but was soon eliminated by the ODSTs. Cal then ordered Private O'Brien to take the shot, so the ODST grabbed the Sniper Rifle and assassinated the prophet, ultimately killing him and his Elite Honor Guards began roaring at his death.
The Prophet's death allowed the United Nations Space Command (UNSC) to regroup and exploit the new weakness in the Covenant supply chain.