was one of the main characters that appeared in the Resident Evil series since the original Resident Evil. She was a member of the S.T.A.R.S. Alpha team in Raccoon City along with fellow protagonist, Chris Redfield. She appeared as the main protagonist in Resident Evil 3: Nemesis as a retired S.T.A.R.S member escaping Raccoon City along with Carlos Oliveira. As the years went on in the fight against the pharmaceutical corporation, Umbrella Chemical, Inc., Chris and Jill would become close allies and full time partners. They would both become heated rivals of Albert Wesker, their treacherous S.T.A.R.S. captain and former Umbrella employee. In Resident Evil 5, Jill and Chris were founding operatives of the B.S.A.A. organization in the fight against bioterrorist plots, continuing their partnership until they were seperated during a fight with Wesker, where Jill was seemingly killed.
On July 23 1998, the S.T.A.R.S. Bravo Team was deployed to the Arklay Mountains located on the outskirts of Raccoon City after evidence of grisly, cannibalistic murders. Alpha Team was sent to find out what happened to their comrades when communication with Bravo Team was lost the day after their deployment. Soon after their arrival, the team found the destroyed remains of Bravo Team's helicopter and were quickly attacked by vicious creatures. After witnessing the death of fellow Alpha Team member Joseph Frost, who was torn apart by a group of Cerberus, the team was abandoned by their helicopter pilot, Brad Vickers, and the remaining members fled to a nearby mansion, secretly the site of the Arklay Research Facility.
Jill, along with fellow survivors Chris Redfield, Barry Burton, and Albert Wesker, assumed the mansion to be deserted. They would quickly discover the various beasts and monsters inhabiting the mansion, as well as the remains of their fallen Bravo Team compatriots. Through her cooperation with Barry, Jill was able to discover that the mansion was actually a front for a top-secret research facility owned by the Umbrella Corporation. They also came to find that Wesker was a double agent working for Umbrella and had planned the whole operation as an experiment to test out Umbrella's Tyrant virus B.O.W.s and to destroy the S.T.A.R.S. team. However, after Wesker was seemingly killed by the Tyrant T-002 he activated to annihillate S.T.A.R.S., Jill and Barry escaped, along with Chris Redfield and surviving Bravo Team member Rebecca Chambers, leaving behind the ruins of the estate, which self destructed.
After their return to Raccoon City, S.T.A.R.S.'s request for a full-scale investigation of Umbrella's activities was denied by their superior, Chief Brian Irons of the R.P.D. With no support from the American government, Chris, Barry, Jill, and Rebecca decided to travel to Europe and investigate Umbrella themselves. Chris went ahead and travelled to Europe by himself by the end of August, while Barry went to Canada to relocate his family first. Jill decided to stay in Raccoon in order to investigate the whereabouts of Umbrella's underground facility before joining her comrades.
However, two months after the mansion incident, her investigation was ruined when Raccoon City was infected with the T-virus. During her escape, she witnessed the death of Alpha team's pilot, Brad Vickers, at the hands of the Nemesis, a Tyrant sent by Umbrella to assassinate the remaining S.T.A.R.S. members. Jill managed to thwart Nemesis temporarily and met with Carlos Oliveira, a surviving member of the U.B.C.S. along with Nicholai Ginovaef and Mikhail Victor. However, Mikhail gave his life protecting Jill and Carlos from Nemesis while Nicholai was presumed dead after an accident. Jill and Carlos ended up in a nearby clock tower after their cable car collided off-course. During the following battle with Nemesis, Jill was infected with the NE-T Virus and was taken to the clock tower's church by Carlos, where she lay there in a semi-coma. Two days later (on the night of October 1st), Jill recovered after being administered with a serum by Carlos, and continued her search for escape.
Soon afterwards, she discovered another one of Umbrella's secret research facilities hidden behind a park. In this lab, she confronted Nicholai for the last time, and fought with Nemesis once again. Jill successfully destroyed Nemesis with a top-secret weapon that was transported to the facility a few days earlier and managed to escape from the city with Carlos in a helicopter piloted by Barry Burton. As they flew away, Jill witnessed the annihilation of Raccoon City on the order of the U.S. government. Jill and Barry would go on to become involved in various anti-Umbrella groups and activities until Umbrella's closure.
After the collapse of Umbrella, rivals and terrorist groups managed to get their hands on Umbrella's projects. With the growing fear of a bio-terror holocaust in Africa, Chris and Jill joined a Bioterror Assessment group partly to locate Wesker who was revealed to be alive when Chris fought him while searching for his sister in Resident Evil: Code Veronica. In 2006, a tip led Chris and Jill to arrest Ozwell E. Spencer, one of the key founders of Umbrella, but when they located him he was already killed by Wesker. Chris and Jill opened fire but were easily taken down by Wesker's superhuman strength. With Wesker ready to deliver a fatal blow to Chris, Jill selflessly tackles Wesker (releasing his grasp on Chris) out the window and descended down the cliffside with Wesker firmly in her grasp.Her body was never found and she was presumed dead. In truth, however she had survived, but was badly injured and unconscious. Wesker then took Jill, and intended to use her as one of the first test subjects in his Uroboros Project. Placing her in cryogenic sleep, Wesker discovered an abnormality within Jill's body: a remnant of the t-virus infection from Raccoon City, which had been reactivated by the cryogenic stasis. As the virus disappeared, it left in its place powerful antibodies, which Wesker then used in order to help make the Uroboros less poisonous, thus giving human subjects a better chance of surviving infection. As a result of the antibody extraction Jill's hair became a light blond color, and her skin became paler due to lack of sunlight (etiolation). After using her to further his virus-development, Wesker then decided to use her as a potential super soldier. His method was to use "P30", a Progenitor-virus based chemical, which granted the user immense strength and speed, but also made them susceptible to control. While P30 had potential, it also lasted for only a short time, due to the body metabolizing it quickly. To remedy this Wesker placed a mechanism on Jill's chest to release a steady stream of P30 into her, in order to keep her under his control, while she hid behind a cloak and beak shaped mask.
While brainwashed and disguised, Jill was sent to assist and keep an eye on Ricardo Irving, an employee of Excella. Chris went to Kijuju to investigate strange happenings somehow involving Tricell, and was introduced to Agent Sheva Alomar, his new partner assigned to aid him in the region she was familiar with. During their pursuit of Irving, Chris found files which included pictures of a blonde woman in a pod who looked like Jill Valentine, giving him hope for her survival. When the pair closed in on Irving's location, he saw them coming from a security camera and fled to a mining area with Jill beside him in an old car. Chris and Sheva followed him to the mining area and soon cornered Irving in his hiding place where he was hiding plans to his operation. As the three held each other at gunpoint, a smoke grenade was all of a sudden thrown into the room, blinding Chris and Sheva. The disguised Jill then swung down, crashed through the window, and grabbed Irving, urging him to hurry. Mocking the agents, Irving was swiftly pulled out another window by the cloaked Jill, who Chris and Sheva did not recognize. While the two escaped, the agents saw where they were going on the documents Irving was guarding: an oil field in the marshlands.
Chris and Sheva went in pursuit to the area in question, attempting to capture Irving while also searching for Jill. They refused to retreat and fought past Irving's forces until they found the Tricell oil facility, where Irving was holed up. Inside the base, Jill gave Irving a briefcase of gold bars as his payment, but he accused the mind controlled Jill as being no more than "one of Excella's playthings". Jill demanded to know how Irving was going to eliminate the B.S.A.A. agents since all other attempts had failed. She strangled Irving and held him up to a wall with one hand, making use of her enhanced strength. She demanded further to know how Irving planned to kill Chris and Sheva. While he continued to mock and insult Jill as a mere servant, Irving was eventually persuaded and convinced her he would handle the situation. Jill released her grip and handed Irving a Control Plaga sample, ordering him to use it as a means of destroying Chris and Jill. Irving tried to avoid the plaga injection by setting off the self destruction of the field to get rid of the agents and fled on his yacht, with Jill accompanying him to the dock one last time. She then jumped down to a speed boat and escaped as Sheva spotted and recognized her from before. The field, being more dry than expected, failed to kill the pair as they escaped and followed Irving. They would eventually defeat the mutated Irving in combat and find out where Jill went from him.
Jill took her speed boat to the cave leading to the underground facility and went to report to Wesker and Gionne. Chris and Sheva arrived and found the boat docked in the cave, remembering the cloaked woman used it to escape and noticing that the key was missing. Jill reported to Wesker and Gionne about the B.S.A.A.'s arrival. Wesker sent Gionne and Jill to deal with the agents while he waited deeper in the center. Eventually, Chris and Sheva came across the pod they had seen within the file earlier, though it was now empty. They were contacted by Excella, who claimed that she didn't know where Jill was. Not believing her, they decided to track her down. They first met Excella in an experimental room deep within the facility with Jill standing beside her in an observation window. Excella told them about some process of evolution as a test subject began to transform into the creature Uroboros Mkono. After the "unworthy" subject fully mutated, Excella and Jill left. When Chris and Sheva defeated Mkono, they pursued Gionne and the cloaked servant. They eventually encountered Gionne in the flesh, and the masked Jill interrupted and nearly overpowered the two agents, despite being outnumbered.
A stray shot knocks away her mask, and Wesker pulls back her hood, revealing her to be Jill Valentine herself. Chris tries to talk to Jill but, under Wesker's control, she attacks him and Sheva with a flurry of hand to hand moves. This starts a battle, where the player has to avoid Wesker for 7 minutes or severely damage him enough to make him flee. During this time, Wesker can avoid virtually any attack thrown at him unless Chris is hiding at the time, while Jill can still be damaged and knocked down. If the player kills Jill, they get a game over screen reading "Your Partner Died", the same as if their AI partner was killed. Wesker gets ready to leave, but upon hearing Chris call Jill's name, Jill resists Wesker’s control. He notes down the resistance, calling it fascinating to be happening at such a late stage and leaves her in great pain. A mechanism on her chest, responsible for injecting her with the P30 serum, is exposed at this point and has to be removed. Chris can try to pull off the device, or it can be shot off. (at a risk though, as Jill dies easily) Released from Wesker’s control but severely weakened, Jill apologizes for her actions, stating that she had no control but was fully aware of everything she did. She tells the pair that they have to leave her behind and stop Wesker. Chris objects, but grudgingly agrees when Jill asks if he trusts his partner. After the pair leaves through an elevator, Jill finally declares that Chris is the world's only hope.Jill alongside Josh Stone will be a playable character in the upcoming downloadable content, Desperate Escape. Taking place after Jill is freed by Chris Redfield, it features the two going through three chapters to get to the helicopter. This connects her freedom from Chris to the helicopter at the end, and also features Jill getting the radio. 
Later, after Sheva and Chris defeat Uroboros Aheri, Jill calls Chris on his video phone and passes along some vital information: Wesker's superhuman speed and strength come from the virus within him, a virus which is kept in balance by a serum he must be injected with. If he can be injected with an overdose of the serum, it should severely damage his body and weaken his abilities. As it happens, the two of them had just happened to come into possession of a vial of the serum earlier in the day, and it is only through application of this serum that Wesker is forced to retreat.
Jill does not appear again until the very end of the game when Wesker falls into the molten lava. Jill, riding in a BSAA helicopter piloted by Josh Stone, throws a ladder out to Chris and Sheva. They climb into the chopper, Chris barely grabbing on before the ground melts into magma. Just as they climb inside the cabin, Wesker desperately reaches out with his mutated arm and immobilizes the helicopter, attempting to bring his most hated enemies with him as he dies. Jill tells Chris and Sheva to use the weapons stored in the the cabin, a pair of RPG-7s. They kill Wesker and release his grip on the helicopter. In the final cutscene in the chopper, Jill simply says "Finally...." in response to Chris saying "It's over...".Jill's standard and most well-known outfit is a pair of blue assault pants with a light blue formfitting shirt and shoulder/neck armor, completed with a blue beret on her head. In addition to her S.T.A.R.S. uniform in the first game, Jill wore a casual outfit consisting of jeans and a black midriff. In Resident Evil: Director's Cut, she wore a sleeveless blouse with jeans and boots as a default outfit in the game's Arranged Mode. The Sega Saturn version of the first game also featured Jill in an alternate version of her S.T.A.R.S. uniform.
In Resident Evil 3, she wears a blue tube top, black mini-skirt and a white sweater wrapped around her waist as her default outfit. This is also a well-known outfit and is the outfit worn by Sienna Guillory in the second film. She has a total of five alternate outfits (eight in later versions), including her original S.T.A.R.S. uniform, an outfit that makes her resemble Regina, the heroine of the Dino Crisis series, a police mini-skirt, a biker outfit, and a disco outfit. The Resident Evil remake featured her standard Resident Evil 3 outfit and a new military outfit modeled after Sarah Connor's outfit from Terminator 2: Judgment Day.
In Resident Evil: Deadly Silence (the Nintendo DS port of the original), Jill gets to wear her original casual outfit, as well as a revealing policewoman uniform in the game's "Rebirth" mode.
In Resident Evil 5, Jill sports a BSAA uniform in a flashback sequence and as one of her costumes in The Mercenaries. This outfit bears some resemblance to her S.T.A.R.S. uniform, with a baseball cap instead of a beret. During the game itself, she wears a tight purple battle suit with a long cloak and a metal, beak-shaped mask.