Helen Marks was a Vault 51 dweller who perished under ZAX's rule. A pre-War surgeon, Marks was one of the few natural leaders locked up in the Vault. When one of the dwellers was strangled for her food rations, then thrown from the balcony, she determined that her death was no accident and insisted on catching the killer by the whole community, but her words fell on deaf ears.
Together with Reuben Gill, she was one of the few interested in the Vault's long term survival even in the face of starvation. Despite the violence that accompanied it, Marks clung to her convictions as late as August 2078, even in the face of the brutal death of the Chambers, Matthew Johnston, and Carmen Greene, the disastrous result of affairs gone very, very bad. ZAX's and Gill's cynical remarks about the food supply stabilized horrified her and she was able to shame Gill into reason.
As a pillar of stability, Marks was a threat to ZAX's plans, which was determined to determine a leader through a process of physical elimination. To remove the obstacle, ZAX poisoned Marks on August 6, 2078. A natural leader was found by her friend, her face buried in a bowl of rationed food. Her death pushed Reuben over the edge, leading to a wholesale slaughter of the Vault.
Helen Marks is mentioned only in Fallout 76.