Sydney Anne Bristow was born to Jack Bristow and Laura Bristow. Sydney believed Laura had died in a car accident when Sydney was only a young girl. At a young age Sydney began displaying a high level of intelligence and Jack began to subtly train her to be an agent someday. Though he never fully intended for her to lead that life, when she was 19 years-old she was recruited to work for SD-6. She was led to believe that SD-6 was a black ops division of the CIA, as were the rest of the agents who worked there. She was under strict orders not to tell anyone about her involvment but she broke that order when she told her fiance, Danny Hecht. As a result, SD-6 Director Arvin Sloane had Danny killed. Sydney was very careful not to tell her friends Francie and Will about her secret life. Sydney spent a few months away from work, causing Sloane to worry. He tried to have her killed but she was rescued by her father, who told her that SD-6 was in fact a branch of the Alliance of Twelve, they were the bad guys. In order to get back into Sloane's good graces, Sydney went on a rogue mission. When she returned, she began working for the C.I.A. as a double agent. With both her and her father working as double agents, Sydney and Jack tried to form some kind of bond between them with Sydney not completely sure she could trust him. She would later learn that her mother didn't actually die. She managed to escape and she was n fact a KGB agent named Irina Derevko. At ther first meeting in nearly 30 years, Irina shot Sydney and then later turned herself in to the government. Sydney eventually falls in love with her C.I.A. handler Michael Vaughn and they have two children together (Isabelle and Jack).
Jonathan Donahue Bristow was originally born in Canada. He joined the C.I.A. at some point in th 1970s. Around that time he met Laura, an English graduate student. The two married and had a daughter, Sydney. Jack would later find out that Laura was in fact a KGB agent named Irina Derevko who was assigned to marry and American agent. After she left, he was put into prison since the government couldn't be completely sure of his loyalties. He was eventually released and began quietly training Sydney as a spy. Along with his good friend Arvin Sloane, Jack joined the Alliance of Twelve, working at SD-6 in Los Angeles. Unlike Sloane, though, Jack remained loyal to the C.I.A. and served as a double agent. Jack was a gifted game theorist who was known to hold grudges. He never forgave Sloane for recruiting Sydney and though he had a weakness for Irina for the rest of his life, he forgave her for her betrayal. Jack's number one priority has always been Sydney, even if his methods weren't always the best. Everything he's done, he's done to protect her.
As a C.I.A. agent, Arvin Sloane became disillusioned and joined the Alliance of Twelve, heading up the SD-6 cell in Los Angeles. He recruited Sydney Bristow, daughter of his friend Jack, against Jack's wishes. He was married to Emily Sloane for over 30 years, until her death. For most of his life Sloane has been obsessed with Milo Rambaldi, a 15th century inventor and prophet. Sloane let this obsession rule his life and his work, eventually letting it cost him everything he loved. He orchestrated the desctruction of the Alliance when it suited him best and after some time in prison, he was granted a pardon and spent his time in Switzerland involved in various philanthropic endeavors. He was later asked by the U.S. government to head a black ops division known as Authorized Personnel Only, much to the dismary of Sydney, Jack and Dixon. A tryst with Irina Derevko years earlier resulted in a daughter, Nadia Santos. Nadia sooned joined her father and sister Sydney at APO and Sloane attempted to leave his obsession with Rambaldi in the past. Eventually the obsession resurfaced, leading to his demise.
Michael Vaughn was originally assigned to a desk job at the Los Angeles branch of the C.I.A. but was promoted when he became Sydney Bristow's handler. Always there to listen when she needed it, Vaughn and Sydney eventually fell in love. When he believed she had died, he married NSC liason Lauren Reed. When Sydney returned, old feelings resurfaced but he remained loyal to his wife. He later found out that his wife was an operative with the Covenant, a group that seemed to have taken over the work of the Alliance. Vaughn eventually killed his wife and was reunited with Sydney. Both worked at APO with Sloane and Vaughn soon proposed and he revealed that his real name was Andre Michaux and he'd been working to discover the goings on of a group named Prophet Five and their involvement with his father's death. Sydney found out she was pregnant and not long after Vaughn was gunned down and killed. He was revealed to be alive right after the birth of his daughter, Isabelle. Vaughn soon returned to APO, working with Sydney to take down Prophet Five, which allowed them to lead a quiet life with their children.
Marcus Dixon was Sydney's partner at SD-6 and was unaware of the divisions true loyalties until it was taken down by the C.I.A.. An intensely loyal man, Dixon had trouble coming to terms with Sydney's knowledge of SD-6's true origins and her failure to tell him about it. He eventually joined the real C.I.A. and became director of a joint task force at the Los Angeles office. His wife Diane was killed when Sloane retaliated for Dixon's accidential killing of Emily Sloane. Dixon never forgives Sloane for his criminal acts and betrayals and questions his every move. He and Sydney remain close, in part because of their shared experiences with Sloane. Dixon later begins a relationship C.I.A. Director Angela Chase. After Sydney and Vaughn's retirement from the C.I.A., Dixon remains in his position and sometimes calls on his friends for help.
Irina Derevko was recruited by the KGB at an early age, quite an honor for a young Russian girl. She was trained and sent to the United States on a mission to marry an American agent. She married Jack Bristow, who never hid the fact that he was a C.I.A. agent from her and sometimes shared some of his work with her. On orders from the KGB, in an effort to solidify her relationship with Jack, Irina was ordered to have a baby. She never wanted to be a mother and when her daughter Sydney was a young girl, Irina faked her death and left. Irina soon rose to prominence as a criminal and then surrendered to the C.I.A. and worked with them to take down Sloane. Her true motives were a mystery until she escaped from C.I.A. custody and went on the run. She was believed to be dead but was in fact being held captive and tortured by her younger sister Elena. A tryst with Sloane resulted in a daughter, Nadia. Like Sloane, Irina was also obsessed with Milo Rambaldi and the two, though they sometimes joined forces, were often at odds to get to Rambaldi arifcats.
Will, a reporter, was one of Sydney's best friends and was also in love with her. When her fiance was murdered Will began investigating the crime. Sydney begged him to stop, as did their friend Francie. Will continued his story and soon uncovered the name SD-6. Not knowing what SD-6 was, Will wrote an article containing everything he did know and gave instructions that it only be published if something wer to happen to him. Sloane wanted Will killed by Jack intervened. Will soon learned of Sydney and Jack's roles as double agents and Will had to destroy the life he had in order to keep living. He admitted to a made up heroine addiction and soon began work as an analyst with the C.I.A.. When Sloane had Francie killed and sent a double to take her place, the double began a relationship with Will. Will was forced into Witness Protection and moved to Wisconsin under the name Jonas. He came out of hiding twice to help Sydney and met up again with the Francie double, Allison Doren, and killed her.
Francie was the good natured friend to Sydney and Will. Francie was a waitress working for a caterer and was engaged to her boyfriend Charlie until Sydney found out that Charlie was cheating on Francie. Eventually tiring of working for other people, Francie opened her own restaurant, which was a success. She was about to begin a romantic relationship with Will when Sloane had her killed in order to place a look alike in Sydney's life.
Marshall worked in op tech at SD-6, believing that he was working for the C.I.A.. He is very fond of Sydney and the people he works with, though he is a little socially awkward. Marshall was sent on his first field mission with Sydney but was kidnapped on his way home. Sydney and Dixon rescued him. When he found out that SD-6 was a branch of the Alliance, Marshall immediately chose to join the real C.I.A. and work with Sydney again. There he met Carrie Bowman, who became pregnant with his child. The two eventually married. Marshall was recruited to join APO and accepted, happy to be reuinted with Sydney and the others. Though not a field agent, Marshall displays great bravery when called upon.
Sark first appeared as an employee of "The Man" before it was revealed that "The Man" was Irina Derevko. His loyalties are flexible, often given to the highest bidder. For a brief time he words at SD-6, completely aware of its true affiliation. He was in league with Irina Derevko until he was arrested by Vaughn. After escaping he joined forces with The Covenant and began an affair with Lauren Reed, falling in love with her. Sometimes he does enjoy helping Sydney and one time does it for no fee at all. Though he has very few morals, he does not actually want to see the destruction of the world.
Eric Weiss was an agent at the L.A. C.I.A. field office and was there with Vaughn when Sydney first walked in. He was quick to pick up on Vaughn's feelings for Sydney and often helped when Sydney and Vaughn needed it. He was shot on a mission in Barcelona but survived. He became more integral once the Alliance was taken down. He and Sydney's friendship deepened when she came back after being believed to be dead for two years. When Sydney's sister Nadia joined them all at APO, Weiss developed feelings for her and the two began dating. With Nadia in a coma, Weiss was offered a job in Washington D.C. just steps away from the president.
Lauren Reed as an NSC liason who eventually married Michael Vaughn. Her father was a Senator. When Sydney Bristow returned, Lauren felt very threatened but helped get Sydney out of custody when she was being tortured. As Lauren's suspicions about her husband and Sydney grow, it is revealed that Lauren is actually working for The Covenant. She is ordered to kill her father but is unable to do it. Her mother, also working with The Convenant, did it for her. Lauren had to scramble to try and keep Michael married to her but he soon found out who she really was. She began an affair with Julian Sark, but his feelings for her ran deeper than hers for him. She is eventually killed by Vaughn.
The product of an affair between Arvin Sloane and Irina Derevko, Nadia was raised in an Argentine orphanage run by a woman named Sofia, who was actually Nadia's aunt Elena Derevko. Nadia had a troubled upbringing and began a life of petty crime. She was arrested and instead of going to jail she was given to opportunity to join Argentine intelligence. She took the chance and excelled. Sydney found her comatose in a mental institution and brought her out of it. Nadia was dismayed to find out her parents were two such terrible criminals and went back to Argentina for a quiet life. Sydney came to her for help with a mission and while Nadia initially refused, she eventually agreed to help and joined APO full time. She begins a romantic relationship with Eric Weiss. She was injected with a compound by her Aunt Elena that turned her into a mindless killing machine. Sloane shoots her to stop her from killing Sydney and she lies in a coma. Sloane is given the ability to wake her by Prophet Five but not long after, when Nadia discovers that he is still obsessed with Rambaldi, Sloane accidentially kills her.
Rachel began much like Sydney did, working for The Shed and being told that it was a black ops division of the C.I.A.. She is taken out of it by Sydney and reluctantly joins APO in an effort to save her own life. She's very intelligent and serves as an analyst while being trained as a field agent. On her first solo mission she has a one night stand with a man she later finds out is Julian Sark. She becomes more and more capable as a field agent and almost begins a romantic relationship with Tom Grace. Rachel is kidnapped by Sloane but is rescued by Sydney.
Thomas Grace was brought into APO after the apparent death of Michael Vaughn. Initially he has trouble working with the team but soon becomes more at ease with them. He gets along particularly well with Rachel Gibson. His wife Amanda was killed and Tom uses APO's resources to get information about who killed her. Tom meets the man and kills him. When Sloane and Sark set explosives through the Los Angeles subway tracks, Tom sacrifices himself to stop them from going off.
Renee, known as the Raven, was a criminal high up on the C.I.A.'s most wanted list. As a child, she was often ill and her father accepted a job from Prophet Five to pay for her medication. He was killed and when Renee grew up, she and Michael Vaughn worked together to uncover the truth about Prophet Five. After Vaughn's death, she worked with Sydney. Originally apprehensive about Sydney, she eventually grew to trust her. Sydney offered her an official position with APO and suggested attempting to get Renee pardoned but Renee was killed by Anna Espinosa.
Kelly Peyton worked with Rachel Gibson at The Shed and was much more deeply involved with Prophet Five. She began negotiating her way further up the ladder and was with Irina Derevko when they were trying to find out from Sydney where the Horizon was. Peyton eventually began working with Sloane and Sark but was caught and imprisoned.