From Halopedia, the Halo wiki
Sadie Endesha is a civilian and a former resident of New Mombasa. She later became the handler for the Huragok Quick to Adjust, who carried the Vergil subroutine designed by Sadie's father to protect her.
Sadie was born around the year 2533. Her mother, who was a passionate public defender, was killed by one of her clients when Sadie was still young. This prompted her father, Dr. Daniel Endesha, to write a sub-program called "Vergil" into New Mombasa's urban infrastructure AI, the Superintendent, to watch over and protect her. She was clearly irritated by Vergil's "over-protective urges," but she also adored him; she was reduced to tears when she was forced to leave Vergil behind to evacuate New Mombasa, telling Vergil that he was all she had left of her recently deceased father.
She and Mike Branley traversed the war-torn New Mombasa during the Covenant invasion of Earth. They managed to escape alive with the help of Vergil. During this trip, she and Mike grew closer together, which hints that a relationship may have formed between them after they escaped the city. She was also relentlessly hunted by corrupt police commissioner Kinsler who murdered her father before Sadie, with the help of Mike and Vergil, left him to be torn apart by an angry crowd. Though she wanted to go back for Vergil, the AI and Mike convinced her to flee on Kinsler's private train with a group of other refugees.
After the war and upon discovering that Vergil was now infused into the Huragok Quick to Adjust, ONI decided to let her become Vergil's handler as Vergil retained his fondness for Sadie even as part of the Huragok. At some point in 2555, she was captured by United Rebel Front forces from Talitsa to lure Vergil into enemy hands before they were rescued by the remnants of Alpha-Nine.
Following the start of the Created conflict and the Subjugation of Earth, Sadie and Vergil were rescued from a secret ONI base on Luna, now under Created control, by elements of Alpha-Nine as part of a secret ONI mission regarding the United Rebel Front. Sadie and Vergil joined Alpha-Nine in their mission, with Sadie's knowledge of AIs, both from working with Vergil and from what she learned from her father, proving useful against Leonidas. Though Sadie was unsure of herself, Vergil helped to reassure Sadie. After the mission, Sadie and Vergil joined the rest of Alpha-Nine aboard the UNSC Infinity.
Personality and traits
Sadie is a dedicated citizen, attempting to enlist in the UNSC defense force despite the high fatality rate. She is shown to be caring, mourning Tom Uberti even though he gave her and Mike away, nearly resulting in her death.
List of appearances