Olivia Rivers was a member of the Order of Mysteries.
Olivia Rivers was the daughter of the famous actress Shannon Rivers and noted Appalachian inventor Frederick Rivers. As a child of great talent, she was provided with the finest tutors to help bring that talent to fruition. However, the high expectations combined with the stress of Shannon's career - particularly in 2077, as the effort to put the Silver Shroud on the silver screen ramped up - caught up with her. Olivia, a young woman struggling under the responsibility, grew sullen and withdrawn. She felt neglected, with her mother's acting career taking precedence over her needs. The cancellation of their traditional camping trip to Seneca Rocks in June that year due to her mother's packed schedule weighed on her heavily, and she looked forward to being able to leave home to go to college. The Great War would interrupt her plans.
The Rivers family survived on their supplies for months. When they finally had to travel to Charleston to replenish their supplies on July 8, 2078, they were accosted by raiders. Although Frederick tried to pay them off with fresh water and now-worthless money, they laughed it off and instead laid hands on Olivia, spurring her mother into action and leading to her overpowering their attackers. Olivia was instantly taken by her mother's heroic defense and asked Shannon to train her. Although Shannon was hesitant at first, her daughter's insistence and Frederick's calm rationale that the world changed and their daughter needs to defend herself worked. As Shannon began venturing out into post-War Appalachia dressed as the Mistress of Mystery, Olivia focused on her training, aiming to become a Mistress of Mystery just like her mother.
The novelty eventually wore off for Olivia. Although initially taken with her mother's adoption of her 'hero' persona, the tipping point came when she adopted three orphaned girls they found rifling through the Rivers' garage. Olivia argued with her mother, reasoning that the family could not save everyone, and demanding to know how they were choosing who to help versus who to pass over. She particularly felt the injustice of her mother sending away Brody Torrance who lived next door and choosing instead to take in three strangers. As Shannon continued to take in orphaned girls, Olivia became increasingly resentful of the situation.
Order of Mysteries
Olivia thought her mother delusional when she founded the Order of Mysteries but was more unhappy with the situation she was put in where she was expected to be a "perfect, obedient little soldier" and "a role model" for the rest of the girls. Despite her reservations, the new Order prospered and training intensified over the next several years, with Olivia becoming the finest assassin trained by Shannon by far.
In her missions, Olivia displayed an immense talent for in combat, regularly going above and beyond the call of duty. In one instance, she performed a flawless raid against the Garrahan Outpost, then went on to clear four sniper nests, a half-dozen beast dens, and a derelict military bunker before finally returning three days late. She dragged her Initiate, Rachel West, along for the ride, despite it being her first time in the field. 
When the Order suffered their first casualty during a surveillance mission on February 7, 2086, Olivia was profoundly affected. The incident contributed to her belief that her mother's endeavors, and especially her response to the death, were meaningless and farcical.
When her mother overlooked her for the position of Mistress of Novices, instead of selecting Eve Devoir, Olivia did not take the decision well. As she reflected on the meaning behind her past six years of subterfuge, she concluded that the only way she would be able to make a real difference in Appalachia was to join forces with the raiders. Her plan was to infiltrate the raider organization and eventually take over from whoever was leading them.
Olivia used her missions with the Order to track the raiders and find an opening into the organization. This opening came in the form of a checkpoint manned by Brody Torrance who her parents had turned away many years before. When Olivia attacked the checkpoint on June 8, 2086, she killed everyone but Brody, leaving him with only a nick to the leg. After they shared information, they agreed to meet again at a remote cottage at the Whitespring Resort to make an arrangement. Brody reported back to his boss, David Thorpe, and planned to play along with Olivia in pursuit of destroying the Order of Mysteries once and for all. Olivia and Brody continued to meet every couple of weeks until Olivia made her offer - she would sell out the Order of Mysteries in exchange for a blank check, to be signed by raider boss, David Thorpe. As proof, she gave Brody the details of an upcoming supply run in Summersville. David Thorpe dispatched five men with Brody to set up an ambush in a do or die situation for Brody.
When Olivia learned that Allison Long had drawn the Summersville supply run, she tailed her to ensure that the ambush was a success. The ambush failed, Allison Long killed two of the ambushers, and Olivia was forced to kill her fellow Mistress herself. Brody returned to David Thorpe with Allison's head and Olivia returned to the Order with her body.
Olivia continued to feed intelligence to Brody and, even though the ambushed Mistresses put up resistance, the raiders began fighting back against the Order. Eventually, she traded a Project Siphon holotape containing the entirety of the Cryptos mainframe to the raiders. The wealth of intel allowed the raiders to kill seven members of the Order in just three months. In response, Shannon Rivers locked down the manor and limited excursions to only the four most senior mistresses: Herself, Eve, Amy, and Olivia.
Around November 13, Seeker Rachel West caught up with Olivia's plan. Backed into a corner, Olivia fought back. As the greatest of the Order's assassins, she slaughtered her way through the ranks of the Order - killing even her father, Frederick Rivers - before finally leaving her mother a parting message, inviting her to one last meeting in the Savage Divide. After leaving a final message to any survivors, Shannon Rivers departed for the last meeting with Olivia.
Olivia and Shannon confronted one another at Seneca Rocks and fought until Olivia mortally wounded her mother. Olivia did not enjoy the victory for long. Brody Torrance, who had been hiding while the confrontation took place, turned on her the moment he realized she was the last remaining member of the Order, revealing that Thorpe had no intention of allowing Olivia into the Raiders since if she could turn on her own mother and the Order of Mysteries, who's to say she would not do the same to the Raiders to take over Thorpe's position? Once revealing that Olivia had outlived her usefulness to the Raiders, Brody shot her and Olivia would die embracing her mother's dead body.
Olivia Rivers appears only in Fallout 76.