From Halopedia, the Halo wiki
This unidentified Prophet is a San'Shyuum Prophet in the Covenant. He controlled the Covenant operation on Ariel in early 2552, intending to recover the Forerunner AI known as the Knowing, referred to by the Prophet as the "silent oracle". However, two ODSTs, Kojo Agu and Taylor H. Miles, made it to the construct before the Covenant excavation teams, and convinced it to self-destruct. Immediately following the Knowing's destruction, the Prophet declared the planet "desecrated" and "soiled", ordering all Covenant troops to pull out and return to High Charity in order to inform the High Council of the relic's loss.