From Halopedia, the Halo wiki
Ava Lang was a human of the UNSC Marine Corps serving as an Orbital Drop Shock Trooper. Born in around 2529 in Chicago on Earth, Lang was the explosives and demolitions specialist of Fireteam Raven, an elite team of ODSTs attached to UNSC Pillar of Autumn during the Battle of Installation 04.
Ava Lang was born around 2529 in Chicago, URNA, Earth. Lang grew up surrounded by technology thanks to her mother's work as a leading engineer for Acheron Security on the Tactical Autonomous Robotic Defense System, and spent much of her time tinkering with projects. Her mother's work eventually inspired Ava herself to study new semi-automated solutions for explosive ordnance disposal.
When she eventually enlisted in the UNSC, her skillset expanded to include the employment of explosive ordnance in more offensive capacities. Her deft decision-making and unflappable resolve eventually landed her a spot in the ODST ranks, where she was soon assigned to Fireteam Raven. By August 2552, Fireteam Raven were assigned to the UNSC Pillar of Autumn for Operation: RED FLAG, and were part of the ship's complement when it made its escape during the Fall of Reach. When the Autumn arrived at Installation 04 on September 19, Lang, and the rest of the team, were assigned by their commanding officer Major Antonio Silva to defend the cruiser from boarding actions. The squad would defend the ODST drop bay and eventually make their way into the ship's corridors to clear out Covenant troops, before being tasked by Wellsley to conduct a spacewalk and man the cruiser's M910 Rampart point defense network, to assist in shooting down Banshees and Seraphs. The team would eventually make their way back to the drop bay, however, and evacuate the Autumn along with the rest of the ship's complement of personnel.
Battle of Installation 04
Lang would land on Installation 04 with the rest of her squad, but separated from the UNSC forces at large who, under Lieutenant Melissa McKay, were capturing the soon-to-be-named Alpha Base. Thanks to a mobile communications uplink with Wellsley, the squad would hike for twenty-eight hours across the surface of the Installation, eventually meeting up with Mckay and her mechanised convoy on September 20th to raid the wreckage of the now-downed Pillar of Autumn, before later joining the UNSC forces at Alpha Base. Lang would proceed to assist in the defense of Alpha Base, before later being recalled to the ice canyons near the Installation's Control Room to deal with a new threat; the Flood. While in the area, Raven would be tasked with keeping the area clear to allow SPARTAN-II John-117 to proceed with his mission to destroy the Installation. With this objective soon completed, the team evacuated via Falcon, though their craft was shot down by a Wraith, eventually crash-landing elsewhere on the ring. The team would hold off masses of Covenant and Flood forces before eventually being extracted by Pelican. 
With the Master Chief now intending to destroy the ring, Lang and the rest of her team were redirected to the wreckage of the Pillar of Autumn once more to hold off an assault by the Covenant and Flood combined, including a Type-47B Scarab. The team would deploy in a M12B Warthog to the site alongside Marine forces, and take down swaths of enemy troops before the Master Chief was eventually able to detonate the fusion engine of the Autumn and destroy the ring, killing Fireteam Raven and everyone else on the site.
Ava Lang sported a purple-coloured variant of the ODST armor similar to those later worn by ODSTs deployed to Installation 00. Her helmet and chest armour displayed notable differences from standard ODST gear, being slightly more angular and form-fitting than standard ODST armor. In her role as a demolitions/ explosives expert, Lang carried explosives in her backback, though was most commonly seen wielding an MA5B assault rifle.
List of appearances