From Halopedia, the Halo wiki
Sergeant Parker was a non-commissioned officer in the UNSC Marine Corps and an Orbital Drop Shock Trooper. Sergeant Parker was stationed aboard the UNSC Pillar of Autumn as part of the ODST detachment under First Lieutenant Melissa McKay in September 2552 during the Battle of Installation 04.
Battle of Installation 04
Like most of his comrades, Sergeant Parker abandoned the UNSC Pillar of Autumn when it was attacked by the Covenant over Installation 04 using an SOEIV to drop down to the surface of the ring. He then assisted in the attack on the mesa that would be Alpha Base.
Later, he led the ODST attachment that accompanied SPARTAN John-117 on the mission to rescue Captain Jacob Keyes, who was held prisoner aboard the Truth and Reconciliation. After being deployed beneath the ship via Pelican Echo 419, Parker and his ODSTs assisted the Master Chief; John felt that the ODSTs slowed him down because they did not have the reflexes and combat skill Spartans had.
Parker was wounded by the spines of a Mgalekgolo in the vessel's cargo bay. Nevertheless, he shrugged off his wound and continued to lead the attack, liberating Captain Keyes from the brig of the vessel.
After seizing the command bridge, an engagement that resulted in the death of Shipmaster Lat 'Ravamee, Parker and his squad stood guard while the Chief pushed forward to the brig where the Captain was being held. Despite the success of the rescue, Parker and his entire squad were killed when two Stealth Sangheili armed with Energy Swords slaughtered them. The Chief avenged his allies before fleeing with the prisoners.
He was an efficient, personable leader. He was also very duty-minded, as he continued to fight even after sustaining a serious wound. He was noted to have teased the Master Chief, whom he treated with more respect than most ODSTs.
List of appearances