Loki

Loki was an Planetary Security Artificial Intelligence construct in service with the United Nations Space Command. It was stationed aboard the Phoenix-class Colony Ship, until it landed on Harvest. Loki took over Mack's processor when the time needed be. Loki is unlike any other AI in that he can trade places with Mack. Besides a few minor variations of the avatar, mainly the eye color but Loki's avatar is clean whereas Mack's is dirty from "working in the field", they look the same. When Harvest was attacked, Loki made the escape plan, destroyed the Tiara and killed Sif.

Trivia

 * Loki is named after the god of chaos in Norse Mythology. He was an adept shape-shifter and could change not only his form, but also his sex, possibly referencing the ability to switch between himself and Mack. In Norse Mythology, he usually plays the role of villain and trickster.
 * There is a group of structures called "The Pillars of Loki", which could be a reference to him.
 * Loki seems to be the only AI with two different egos; himself and Mack.