Sergeant-Major Elizabeth "Ella" McKenzie served on a multitude of nplanets throughout the Human-Covenant war. She was assigned to Emergencyn Fireteam Theta, one of the several teams posted for the defense of nUNSC Outpost Omicron. Due to then unusually high number of Forerunner nobjects, structures, and non-hostile sentinels n(that had attracted the nUNSC there) they UNSC expected a covenant strike team to attack. They nwere lethally right.

McKenzie fought with the rest of Theta in an series of 18 skirmishes against the Covenant strike teams raiding the nbase. When Steven was wounded, she ordered the rest of the marines to nretreat to the facility. She and Ethan then broke the Covenant perimetern around the base.

Both the fearless leader and Team Ace, McKenzien has little patience for incompetence or lack of skill, resulting in a nfair amount of contempt for Steven. However, she is a loyal officer and nis primarily concerned with the safety of the soldiers under her command