Sif

Sif was a UNSC Shipping Operations A.I. on the Tiara Space Station, in orbit above Harvest. Near the center of the Tiara was a room which housed her data center that contained the processor clusters and storage arrays that served as her core logic.

Chosen Avatar
Her chosen avatar is in the form of a woman with an ankle-length sleeveless gown and long golden hair(it is also mentioned that she has a red poncho that she drapes over her shoulders); she also has the appearance of Nordic royalty. She chose this avatar because many of Harvest's settlers were from Earth's American heartland, who could trace their ancestry back to Scandinavia. This may also be due to the human that she was flash cloned from, as she was implied to be from a European country. This could have also affected her avatar's hair as her human counterpart loved her blond hair which corresponds to Sif's avatar's hair color.

Role
She is in charge of Harvest's shipping operations which included the balancing of the Tiara, the transporting of human and shipping traffic up and down the space elevator, and control of the passenger and cargo transport in and out of the Tiara, as well as shipping manifests and keeping cargo on schedule. The A.I. Mack flirts with Sif often, usually to her annoyance and frustration. Deep down however, Sif enjoys Mack's flirtatious interruptions. This was revealed right before the A.I. Loki took over Mack's internal processing units. Sif occaisionally looked back to her human counterparts mind. She tended to find this entertaining but all she could remember was her hair brush.

Right before the Tiara was destroyed above Harvest, Sif, after being destroyed by Loki, was revived by the Huragok, Lighter Than Some and during the ensuing events went rampant. She died right after she told Mack that she loved him, but it is unknown if her message got through to him, although it is known that Mack loved Sif. Soon after, Loki shot a Mass Driver round into her data center, destroying her and the Tiara. She died contently, after attempting to go through many emotions that her Rampancy afforded her, but she found them all to be untrue to her. She felt that she lived a fuller life than her makers ever thought she would have before dying. She may have gone rampant due to the damage to her proccesor clusters. Despite her rampant state, she chose to help even though she was severly weakened and couldn't do much. When Loki was unable to rebalance the load after losing the number 7 strand due to being weakened by a Brute attack, Sif offered her help and together the two AIs rebalanced it. When Loki decided to destroy her, she agreed and helped him convince Mack to allow it.

Trivia

 * Sif is the wife of Thor in Norse mythology.
 * In Norse mythology, Sif and Loki factually did not correlate with one another often. In the Myth, The Treasures of the Gods, Loki managed to get into Sif's locked bedroom and hacked off all of her golden hair as an unfeasible prank. Thor eventually caught him and made him retrieve fake hair from the Dwarves. Just like in Halo: Contact Harvest, Sif is constantly irritated with Mack or rather (Loki's) presence, comparable to their Norse mythology predecessors.
 * Sif was one of the few AI that went rampant, ultimately ending in her destruction and demise on Harvest.
 * In the Contact Harvest audio book Jen Taylor, the voice of Cortana, takes over the narration when Sif is the focus of events.