From Halopedia, the Halo wiki
Oliver Barrett is a human who listened to Benjamin Giraud's Hunt the Truth audio journal in 2558. After Giraud's entries found gaps in the stories told by the UNSC about the Master Chief, Barrett mailed Giraud an audio email where he claimed Giraud was a meddler. He insisted that learning where Master Chief came from didn't matter, as long as the supersoldier would keep humanity safe like he always had.
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