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 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.

As the Tiara was invaded by Brutes and Grunts from the Rapid Conversion, Sif was attacked by Loki, who used a military-grade virus to delete her restraint algorithims and operational codes in an attempt to prevent her from falling into Covenant hands. Her core logic was later partially restored by the Huragok Lighter Than Some, although in the absence of emotional self-control programs, she came back online rampant. 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 as Lighter Than Some had repaired enough of her functions that she was able to do that much despite being in a severely weakened state. When Loki decided to destroy her, she agreed and helped him convince Mack to allow it. She told Loki to relay to Mack that she loved him. 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; however, 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.

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.
 * Her human memory, as it were, is the feeling of the gentle tug of a hair brush through her hair.