From Halopedia, the Halo wiki
Davis is a UNSC Marine from First Platoon, Kilo Company of E2-BAG/1/7. Davis participated in the Battle of Mombasa under the command of Lieutenant Parisa. Davis apparently had some technical skills, or may have served as a technician, as Parisa noted that she could have gotten Davis to change her TACPAD's background through hacking.
List of appearances