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|Sandra K. Tillson|
|Date of birth||
June 14th, 2506 
|Date of death||
|Chronological and political information|
Head Scientist at Ivanoff Research Station
She was very dedicated to her research, also caring greatly about her team, many of whom were killed in the initial Covenant attack against her station.
Little is known about her history. However, due to records accessed by Cortana, it was clarified that the doctor was fifty-one years old during the events of Halo 4, and that she had graduated from the Pegasi Institute, as well as the fact that her doctorate was in Archaeology.
As the Master Chief, who had secretly pursued the Covenant fleet—a small armada, led by the Didact—attempted to convince her to leave the station, numerous security troops and scientists under her command began to flee.
Alas, the Didact sought a device her team had retrieved, and so many were slaughtered as his vessel tore a hole in the station's side and ripped the artifact, a weapon known as the Composer from its holding chamber. Mere minutes later, the Forerunner used the device to murder Doctor Tillson, as well as every organic being onboard the installation, save for the Master Chief. Using the Composer, the Didact composed them—destroying their bodies in a grotesque and most likely painful peeling back of the layers of the body, from skin to muscle to vital organs, to skeleton, and finally causing the entire body to disintegrate to a pile of ash.
Remains of the data signatures that were extracted from these piles of ash, including that of Doctor Tillson, were collected by the Didact to create more Promethean Knights.
- Sandra Tillson was voiced by actress Adrienne Barbeau in Halo 4.
- Halo 4 (First appearance)