From Halopedia, the Halo wiki
Philip Mistral was a drill operator employed by the Liang-Dortmund Corporation. He took the job with the company against the advice of his brother, who told him it was a bad idea. He was sent to the glassed Outer Colony of Meridian and assigned to a team working to rehabilitate the moon. He left recordings of himself wherein he expressed his satisfaction with Hydrostatic gel technology Liang-Dortmund procured from the United Nations Space Command. He also noted that he regretted signing onto the job due to the nature of a working and living environment that wasn't conducive to healthy breathing.
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