From Halopedia, the Halo wiki
Preston Thorne, also known as "Lieutenant Weephun", is one of the civilians living in 2004's United States who answered the Operator's calls for help. He gained great infamy as the person who betrayed The Sleeping Princess by informing the Operator where she was hiding. At the time of the betrayal, Lt. Weephun decided that his loyalty to the Operator was more important than any feelings that he had towards The Sleeping Princess.
In Melissa's farewell letter, the Operator gave a "Special commendation to Lt. Weephun for hunting down the "Sleeping Princess".
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