Dr. Halsey is a civilian specialist. At the start of the novel, Dr. Halsey is aboard the Hans with Lieutenant Keyes. Keyes is there to pilot the vessel and to protect Dr. Halsey from harm. Dr. Halsey is a civilian, but she is working on a mission with the military, the USNC.
She has very pale skin and dark hair. She also has blue eyes. At the beginning of the novel, she is relatively young and slender. Lieutenant Keyes thinks of her as a striking woman. As the novel continues, Dr. Halsey ages. Toward the end of the novel, Spartan John, who is Master Chief by then, notices that she has aged significantly. Her dark hair turns gray.
Dr. Halsey is working with the military to create super-soldiers. She is genetically augmenting the children she chooses and abducts from their lives. John 117 is one of the children Dr. Halsey chooses. She uses the augmentation process to create soldiers that are tougher, faster, and more intelligent than the average human soldier. The concept is supposed to help the humans win the war against the aliens.