Ellen Santiago held the rank of colonel before the Great War. She was the leader of a large military unit stationed in Washington, D.C. mere days before the Great War. When the bombs began to drop, she led her unit to relative safety, but was always trying to find a way forward from the horrors of the Great War, and the impact the Great War had on her unit.
With no direction from other military personnel, or any idea how to fully escape from the nightmare that was the Great War's aftermath, she led her unit away from the ruins of D.C. toward Appalachia after hearing rumors of a possible safe haven, underneath The Whitespring Resort. When she arrived, she was promptly lured in by Thomas Eckhart, promising revenge against communist China.
As Eckhart's plan to eradicate communism by any means possible rapidly progressed after he successfully became nominal President of the United States, Santiago had to accept Eckhart's dominance over the bunker, but she began to reconsider on whether coming to the bunker without fully understanding the occupants' intentions was a good idea or not.
Santiago was sent to the nearest military installation, Camp McClintock, by Eckhart, to gain an automatic promotion to general, after the previous general within the bunker had died due to poisoning. Eckhart had Santiago accept her promotion, whether it disgusted her or not to wear unearned stars on her uniform.
Santiago later confronted Eckhart, when he tried to ravage Appalachia with super mutants and the Scorched Plague, to increase the DEFCON level to 1, to allow him to use the nuclear weapons within the bunker. She realized that revenge on the Chinese wasn't worth such as steep price, and in 2084 she threatened to leave the bunker with her men.
After Eckhart's usual flattery on the general didn't make her budge on her decision, he incapacitated her with a knockout agent, keeping her in an induced coma, only reviving her if he needed her clearance to further advance his plan.
Not too long later, one of Santiago's subordinates, Major Ragnarsdottir, staged a rebellion in the bunker, due to Eckhart's lack of care for the inhabitants within the bunker, in which Santiago was released from her induced coma and Eckhart was arrested.
Ragnarsdottir planted multiple explosive charges on MODUS, in an attempt to destroy it, so they could leave the bunker freely, without MODUS acting as a firewall toward their plan. This backfired when MODUS was not destroyed, but severely damaged and henceforth corrupted, and in retaliation it intentionally destroyed the weapons lab, which resulted with the immediate death of Santiago, followed by the suffocation of the other inhabitants later, from the leakage of chemicals within the weapons lab that had entered the air supply of the bunker and the subsequent sealing of the bunker; an action performed by MODUS.
Ellen Santiago is mentioned only in Fallout 76.