Rebecca Chambers is the youngest member of the S.T.A.R.S. unit and is assigned to Bravo Team. She is the S.T.A.R.S. field medic and also the helicopter mechanic.
As Resident Evil 0 begins, Rebecca is dispatched alongside her team to investigate bizarre incidents that are occurring in the Arklay Mountains near the old Spencer Mansion. As they near their destination a malfunction occurs and the Bravo Team helicopter crashes. The team, save the pilots, survive and comes across a wrecked military transport. They learn that former Marine Lieutenant Billy Coen, now a condemned murderer, was being transferred to death row when the transport came under attack from an unknown enemy. The soldiers who were guarding Coen were apparently mauled to death, their weapons are missing and Billy's body is not among the corpses present. Bravo Team fans out to begin searching for the escaped convict.
Rebecca becomes separated from the group and stumbles upon a passenger train, the Ecliptic Express, which had stopped in the middle of the forest. Deciding to explore the train, she soon finds that it is full of zombies, and one has fatally wounded her teammate Edward Dewey. Rebecca is rescued from a zombie's attack by Billy Coen, who suggests they team up to have a better chance of survival. Soon after, the train starts moving again, ultimately bringing them to a secret training facility set up by the Umbrella Corporation to test the effects of the T-Virus. While exploring the facility, Rebecca gains the trust of Coen, who insists that he is not guilty of the crime he was sentenced to death for, and protects him from Bravo Team leader Enrico Marini by lying about his location. Unbeknownst to Rebecca or Billy, the duo are under observation by William Birkin and S.T.A.R.S. Alpha Team leader, Captain Albert Wesker, in a secret security room.
After fighting through the underground facility, Rebecca and Billy find a tram car to take them even deeper into Umbrella's underground labs, and it's here where they find Dr. James Marcus, one of the founding members of Umbrella, who had been murdered by his traitorous associates, only to be resurrected by his genetically modified army of leeches, the initial carriers of the T-virus. The renewed Marcus, altered by the leeches as they revived him, now had the ability to control them with mental commands, and it is he who had been commanding the smaller leeches throughout the game. However, the unstable nature of Umbrella's genetic modifications causes him to further mutate right before their eyes into a massive, disfigured "Leech Queen". Upon defeating the Queen, the duo escape the facility just before it self-destructs, and Billy and Rebecca go their separate ways, with Rebecca reporting to her superiors that Billy died in the facility, taking his dog tags back as evidence. Billy then escapes into the forest (to date, the last time he was seen in the Resident Evil storyline) and Rebecca, after learning that the S.T.A.R.S. survivors had shacked up in the Spencer Estate, heads toward the mansion to rejoin her teammates.
Rebecca enters the Spencer Mansion, and upon finding it totally deserted, heads to a bedroom to crash and get some well needed R&R after all the excitement. After waking from a nightmare in which she is menaced by snakes, she finds her Bravo teammate, Richard Aiken, and together they further explore the mansion but again, they get split up. This is where her events in the first game really begin as she returns to the main hall of the Mansion where she meets up with Alpha Team member (and one of the two protagonists of Resident Evil), Chris Redfield.
Rebecca has a lot less story driven moments and instead mainly serves to help Chris solve puzzles such as mixing chemicals and, inexplicably, playing the Moonlight Sonata to help open a passage. The duo find Richard wounded after an encounter with Yawn (a giant snake). Richard dies from the wounds but Chris manages to drive away the snake, and a distraught Rebecca must soldier on if she wants to escape the mansion and survive.
Rebecca and Chris are taken by Wesker, who reveals that he engineered these events to acquire combat data, to see the Tyrant. When the Tyrant awakens and "kills" Wesker, Rebecca aids Chris in defeating the hideous monster. After Chris frees Jill Valentine, Jill and Rebecca hold off the zombies while Chris signals Brad Vickers for a pickup.
While the trio await Brad, the Tyrant re-emerges and attacks the group. Having mutated into a stronger version than before, the small arms fire that they are using have little to no effect on the Tyrant. Brad tosses Chris a rocket launcher and using it destroys the beast once and for all.
An exhausted Chris, Jill and Rebecca escaping in the helicopter moments before the mansion is destroyed in an explosion.
Resident Evil: The Umbrella Chronicles attempts to re-tell the storylines of Resident Evil Zero and the original Resident Evil, among others . In the Zero segment, Rebecca is teamed once more with Billy Coen; upon defeating Doctor Marcus she is ordered to fall back to the Spencer Mansion. There she finds a safe room with a cot to hold up in. She witnesses Sergei Vladimir removing the U.M.F.-013 and the Ivans defeating the Cerberus Hounds. She then falls asleep and has a nightmare about the giant snake Yawn before actually encountering it. She is then reunited with fellow Bravo Team member Richard Aiken. The duo fight their way through the mansion until they come under attack by Yawn. Richard and Rebecca battle the snake in the library until Richard is wounded saving Rebecca. The duo themselves are then saved from Yawn by Chris Redfield and Jill Valentine but not before Richard succumbs to his wounds.
[Note: Rebecca witnessing Sergi removing the UMF is canon, as is her nightmare of the snake before meeting it. Only scenarios that would retcon previous events of the series are considered non-canon]
Rebecca hasn't made an appearance in the Resident Evil series since the first game (Chronologically). In Resident Evil 2, her name is mentioned in passing, in a comment which confirms she survived the mansion incident and is alive, but besides Resident Evil Zero, her only other real appearance is in Umbrella Chronicles on the Nintendo Wii. This is a retelling of much of the series, which documents several chapters of Resident Evil Zero as a first person shooter. One thing of note is that in this game, she was modelled after Ayumi Hamasaki, a popular J-Pop icon. Rebecca is also one of the playable characters added to Resident Evil 5's The Mercenaries mode in the special edition, known as the Alternative Edition. This lets players play through The Mercenaries as Rebecca, alongside other characters such as RE1's Barry Burton and RE5's Excella Gionne. Rebecca's appearance in this mode is based off of her appearance from Resident Evil Zero. Like all The Mercenaries characters, Rebecca has a unique loadout, voice, and melee attacks. However, as The Mercenaries is just a minigame, it is considered non-canon; Rebecca Chambers did not really fight Majini in Africa, and her current whereabouts remain unknown.
While she has not been mentioned post-Resident Evil 2, Rebecca has been featured in several non-canon books by author S.D. Perry, including the adaptations of Resident Evil Zero and Resident Evil (this is based on the original RE1, not the Gamecube-exclusive remake).
She has also been featured in several stories of the late 90's Resident Evil Comic Series by Wildstorm Comics