From Halopedia, the Halo wiki
Likely Office of Naval Intelligence
Oberon 5 was likely an Office of Naval Intelligence agent. While aboard Midnight Facility on January 15, 2553, this individual interrogated Alo Sebukah, a San'Shyuum former Vice Minister within the Covenant, regarding his brief interaction with Cortana during the Fall of High Charity two months prior.
The officer's real name, rank, and gender are unknown. In medieval and Renaissance literature, Oberon is the name of the legendary king of the Breton fairies.