From Halopedia, the Halo wiki
Office of Naval Intelligence
Commander Irvin Yarick is an Office of Naval Intelligence officer.
During her ONI sessions, Melody Azikiwe received additional training from Commander Yarick. He showed her how to rapidly cycle a cryo chamber without irreparably damaging its contents, just in case Melody didn't have another choice.
After the conclusion of the Carrow Conflict, Yarick met with Gray Team aboard the UNSC Welcome to the Snipehunt where he stated that he would be their new ONI liaison. He offered the team a deal to work with a new specialized interspecies strike force in the Joint Occupation Zones in exchange for their being pardoned for their war crimes. He later met with Rear Admiral Serin Osman and reported to her on the situation on Carrow.