Sentinel Lyons

Sentinel Sarah Lyons is a high-ranking Brotherhood of Steel officer and the commander of the elite Lyons' Pride squad in 2277. She became elder upon the death of her father, Owyn Lyons, but was subsequently killed in action.

Background
Sarah Lyons was born in 2251 in the Brotherhood of Steel's Lost Hills bunker in California. In 2254, the Brotherhood of Steel ruling council decided to send a contingent of soldiers under the command of Star Paladin Owyn Lyons to the East Coast with a mandate to recover all advanced technology from the Washington, D.C. area. Three at the time, Sarah joined her father on his journey east to the Capital Wasteland (her mother having died several years earlier). Since their arrival and establishment of a permanent base at the Citadel, Sarah trained to be a warrior.

By 2277, Elder Lyons' daughter Sarah is a grown woman and one of the Brotherhood's finest warriors. Brotherhood through and through, she is as dedicated and decorated as her father when he was younger. In fact, she's the only member to have achieved the illustrious rank of sentinel, and now commands her own elite squad, Lyons' Pride.

Sarah Lyons routinely went on routing super mutants from their various raiding posts in the Capital Wasteland and would later help the Lone Wanderer defeat the Enclave during the battle of Project Purity, storming the purifier at the head of Lyons' Pride and just behind Liberty Prime.

Sarah fought for her father's chapter of the Brotherhood of Steel until his death. Afterwards, she became the new elder of the East Coast Brotherhood. Despite her essential leadership position, Sarah continued to fight on the frontlines. Shortly thereafter, she was killed in combat and Lyons' Brotherhood of Steel would struggle to find an effective leader for several years until the rise of Elder Arthur Maxson.

Personality
Sarah is loyal to her father, but her superior attitude to wastelanders is more typical of those in the Brotherhood with lingering sympathies for the Outcasts. She has little patience with "civilians" stumbling into the line of fire. Her attitude towards Initiate Reddin suggests she is not convinced that wastelanders should be recruited into Brotherhood ranks.

Despite this harsh attitude towards outsiders, Sarah cares about the people of Capital Wasteland as much as her father does, and will not hesitate to protect anyone that needs help. Additionally, fighting alongside the Lone Wanderer has made her more tolerant about wastelanders.

Like many of her Brotherhood companions, Sarah loathes super mutants.

Quests

 * Following in His Footsteps: The Lone Wanderer encounters Sarah while traveling to the GNR building plaza. The player character will find her squad not far from the Tenleytown/Friendship station exit to Chevy Chase North. When the player character approaches her, Sarah will not trust them but will allow them to follow behind them to the GNR studios. Upon reaching the GNR building plaza, the Lone Wanderer and Lyons' squad will be attacked by super mutants and a super mutant behemoth. Lyons will then enter the GNR building with the remainder of her squad. While there, she can be talked to and will thank the Lone Wanderer for their help if appropriate.
 * The Waters of Life: Sarah accompanies her father when he receives Dr. Li, her team, and the Lone Wanderer at the Citadel's courtyard. Once the Elder has finished his conversation with Li, Sarah will unsuccessfully try to convince her father to let her team attack the Enclave immediately.
 * The American Dream: Once the Lone Wanderer has escaped from (and possibly destroyed) the Enclave's base at Raven Rock, Sarah will once again attempt to convince her father to let her team try to retake the Jefferson Memorial. While Elder Lyons initially refuses, once he hears that the Enclave has acquired the G.E.C.K. and thus possess the technology to reactivate Project Purity, he agrees to greenlight the mission.
 * Take it Back!: Sarah, after inducting the Lone Wanderer into the Pride, briefs her team on the mission to come. She personally accompanies the Lone Wanderer into the Jefferson Memorial rotunda for the final confrontation with Colonel Augustus Autumn and his handful of personal guards. Based on the Lone Wanderer's choice, Sarah Lyons will:
 * Watch the Lone Wanderer's selfless act of sacrifice in choosing to enter the chamber and mourn their inevitable demise (unless Broken Steel is installed).
 * Enter the chamber herself, sacrificing herself in place of the Lone Wanderer.
 * Wait until the purifier explodes.
 * Who Dares Wins : After the player character escapes from the mobile base, Sarah Lyons will appear again (unless she was killed) and pick the Lone Wanderer up in a vertibird, taking them back to the Citadel.

Effects of player's actions

 * She will comment if the player character is wearing power armor when fighting the behemoth in the GNR plaza, saying they can wear it for helping them defeat it.
 * If the Lone Wanderer activates the purifier themself, or uses Fawkes, Sergeant RL-3 or Charon to start it; it is revealed that an energy spike knocked her and the Lone Wanderer unconscious. Two weeks later after the Lone Wanderer wakes up, she's still in a coma, "unresponsive but stable."
 * If Lyons activates the purifier, she will be killed by the radiation and does not appear again.
 * After completing all the main quests, if the Lone Wanderer chooses to destroy the Enclave, she will comment that if things had been different, they could have had time to become friends.
 * If the Lone Wanderer betrays the Brotherhood instead and launches an orbital strike on the Citadel, she and the other Brotherhood members who picked the Lone Wanderer up will attack in a fury, calling them a traitor. It is then possible to kill her, as she will no longer be essential.

Appearances
Sarah Lyons appears in Fallout 3 and its add-on Broken Steel, as well as a legendary dweller in Fallout Shelter. She is also mentioned in Fallout 4.

Behind the scenes
Fallout 3 Faction Profile – the Brotherhood of Steel (archived) by Emil Pagliarulo.

Bugs

 * At the end of the game Sarah Lyons can glitch into either saying that "the control room still isn't clear" or repeat the phrase "Steel be with you!"
 * After The Waters of Life, before speaking to Rothchild to start the quest Finding the Garden of Eden, Lyons will appear on the road leading from Arlington Library to the Flooded Metro, walking along the road to a point past the Nuka-Cola plant.