His chosen avatar is that of an American cowboy, exactly as those from old western movies from the 20th century. He usually has messy black hair and he wears cracked leather work boots, blue denim jeans, a gingham pearl-snap shirt rolled up to his arms, and a sun-bleached gray cowboy hat. He usually presents his avatar covered in dust and grease, to promote the idea that he has been hard at work. He is lighthearted and speaks in a western drawl.
Mack is the AI in charge of all of Harvest's agricultural operations. These planetary operations include the control of the JOTUN harvesting devices which are used for planting, maintaining, harvesting and packing of agriculture on Harvest, as well as preparing the produce for its journey up Harvests space elevators.
He is well liked by the population of Harvest and is said to be everyone's favorite uncle. He helps the people of Harvest with their problems and offers free advice about a problem before it even becomes known to the person who has the problem. During the evacuation of Gladshiem, the people of Harvest wanted him to appear as his mere presence calmed and comforted them.
He often would playfully "flirt" with Sif, eliciting strange responses in the female AI, seemingly of hate but tinged with an unexplainable feeling analogous to human attraction underneath. Eventually, he reveals to Sif that he is not one but two AI's, his counterpart being an AI known as Loki, originally the AI of the UNSC Skidbladnir, a Phoenix-class colony ship which transported Harvest's first settlers.
Battle of HarvestEdit
When the combined Covenant Army and Navy force pressed their attack on Harvest, he gave over his control to Loki, transmitting "himself" into the thousands of JOTUN machines below. He instructs Loki to keep Sif safe, but Loki disagreed and believed she should be destroyed in order to prevent her data falling into alien hands. Loki disabled her, but she was repaired by the alien Lighter Than Some.
Mack versus LokiEdit
Mack eventually rebelled against Loki, resisting his attempt to activate a ground-based mass driver, an early, ground based version of the Magnetic Accelerator Cannon, which Loki was trying to use to destroy the Tiara, as well as Sif's data center so that she would not fall into the Covenant's hands. His sudden attack also saved Loki as he destroyed the Covenant forces assaulting the data center. Mack managed to temporarily regain control of the data center and destroy Loki's fragment on the Tiara with a virus in an attempt to save Sif, but Loki quickly regained control. He caused some problems as Loki, in his weakened state was unable to re-balance the Tiara which his fragment may have been able to accomplish; however, Sif (repaired by Lighter Than Some) was able to help Loki accomplish this. Mack's all-in-ones hacked Loki's maser and destroyed Loki's fragment on the Tiara (as revenge for harming Sif). Mack tried to bring Sif down into his machines, but there was too much damage to her arrays (thanks to Dadab wrecking the data center with his Plasma Pistol). Loki eventually regained control in time to destroy Sif with the mass driver.
An ONI ship later recorded Mack's final transmissions, extremely disjointed and rampant words that he transmitted to the destroyed Sif as the Covenant burnt his world. He continued to resist, but as his resources dwindled he made a last desperate attempt to help his now destroyed "love" Sif by burying her fallen Space Elevators.
By the time the Covenant attacked, Sif and Mack were both slightly rampant. Knowing this, Sif accepted her fate when Loki destroys her.
His final transmission was that he will "Bury your strands so deep their fires can't reach them and glass them like the rest".  His final words were a misquoting of Shakespeare, a habit he had that both annoyed and charmed Sif during their time together.
Although he knew Sif cannot hear him he claimed that it keeps him busy while the Covenant slowly destroy Harvest.
He was undoubtedly destroyed as he said that the Covenant were destroying his JOTUN's. They likely destroyed them all, and him along with it.
- Halo: Contact Harvest (First appearance)
- If Loki had not destroyed Sif, the Covenant would have captured her and extracted the coordinates for Earth. The Covenant would have arrived at Earth a lot earlier than if Loki had not destroyed her. Had the Covenant found Earth's co-ordinates that early into the Human-Covenant war, the UNSC would have been ill prepared and extremely vunerable, still under great opposition from the Insurrection. The events that Loki set into motion most likely changed the outcome of the war.