Brian K. Ellis was a Weyland-Yutani Corporation employee working as a technician with the company's Berserker program. He was a member of the Berserker hunter/killer team dispatched to DS 949 in response to the Xenomorph outbreak there.
He was stationed on board the Nemesis for his first tour. He was one of three survivors after their disastrous mission to W-Y facility Station 949. During the mission He was rescued along with Jess and Lara later being held by Weyland-Yutani workers on Bunda while waiting for an executive from the company to be debriefed on the Nemesis.
Ellis and the other survivors escaped when a Yautja hunting party released xenomorphs on the planet's surface hunting human and xenomorph alike. Ellis and the others were rescued by Machiko Noguchi; who had spent a year amongst the hunters, only to turn on them when the hunt was going to focus on humans. Ellis, Noguchi, Jess, and Lara survived the three way fight with Ellis going into the berserker unit again, attacking both Yautja and Xenomorph alike before leaving the unit planetside.
Sometime after their evacuation, Ellis and Machiko create and manage a remote colony prior to being approached by the United States Colonial Marine Corps for assistance with the Predator race. Ellis leads a small strike force composed of the colonists when aiding Machiko with the joint operation between the USCM and the Predators, and later becomes romantically involved with Machiko.