From Halopedia, the Halo wiki
Al-Thani was an Orbital Drop Shock Trooper stationed on the UNSC Pillar of Autumn during the Battle of Reach and the Battle of Installation 04. They were a member of First Lieutenant Melissa McKay's unit. They were killed in action when the Covenant intercepted and boarded the ship. Judging by the way Valdez's face was covered in Al-Thani's blood, it was most likely Al-Thani was critically wounded in battle, and the medic had attempted to save them but was unable to.
List of appearances