"Jill Valentine is a main character in the Resident Evil series of survival horror games. She is one of the most prominent human characters in the franchise and one of the most popular characters. She has appeared in other Capcom games in the form of a cameo or a crossover appearance.

Jill was one of the heroes in the original Resident Evil, where she was introduced as a member of the Special Tactics And Rescue Service, part of the unit's Alpha Team. She was in charge of rear security and specializes in bomb disposal (an ability she acquired as a Delta Force operative). She returned as the main protagonist of Resident Evil 3: Nemesis, where she was no longer a member of S.T.A.R.S., merely a citizen trying to survive the viral outbreak in Raccoon City. She is also a current BSAA member who co-founded including Chris Redfield and nine others for the organization. In Resident Evil: Revelations and onwards she works as a Special Operations Agent.

Jill's depiction over the course of the series has gone through minor changes while still maintaining a level of consistency. All of her default outfits are variations of blue. Her dress attire ranges from tactical gear to sleek.

In the original Resident Evil, her hair was long but tucked into her beret, while in the Resident Evil 3: Nemesis, Resident Evil: The Umbrella Chronicles, and Resident Evil: Operation Raccoon City her hair was in a bob. Resident Evil 5 marks the introduction of Jill going from brunette to blonde as a result of experimentation done on her body. In her most recent appearance, Jill is shown to have grown out her hair and tie it up in a low ponytail similar to Claire Redfield's hairstyle in The Darkside Chronicles. In Resident Evil: Revelations, a prequel to Resident Evil 5, her hair is brown again but still in a ponytail.

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 wears a casual outfit consisting of jeans and a black shirt. In Resident Evil: Director's Cut, she wears a sleeveless blouse with the S.T.A.R.S logo on the back along 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: Nemesis, she wears a blue tube top, black mini-skirt, white sweater wrapped around her waist, and brown tactical boots as her default outfit. This is also a well-known outfit. It later became her Nostalgia outfit in the 2020 remake version only to be added with a gun holster on her right thigh and her mini-skirt was extended below her knee. She has a total of five alternate outfits (eight in later versions), including her original S.T.A.R.S. uniform, a police mini-skirt, a biker outfit, and a disco outfit. The Resident Evil remake featured her standard Resident Evil 3: Nemesis outfit and a new military outfit.

In the 2020 remake version of Resident Evil 3, Jill's original outfit has been updated; her blue tube top is replaced with a blue V-neck sleeveless shirt with a white tank top underneath, no longer wearing a white sweater tied to her waist. Her black mini-skirt is replaced with dark gray jeans with a brown and her black tactical boots resembling combat boots. She also uses a black necklace on her neck. She later gains both a shoulder holster, a gun holster, and an utility belt where she keeps her firearms as well as a pair of black fingerless gloves and a black elbow band on her left after Brad lets her escape. At the end of the game, she is no longer wearing her tactical gear within her main outfit, instead, she wears a lime green tank top and her charcoal gray jeans.

In Resident Evil: Deadly Silence (the Nintendo DS port of the original), Jill wears her original casual outfit, as well as a revealing policewoman uniform in the game's Rebirth Mode.

In Resident Evil: The Umbrella Chronicles, Jill wears a purple and blue vest along with white jeans and snow boots. This winter attire is reminiscent of her mission being set in Russia.

In Resident Evil: Revelations, Jill wears a pale blue long sleeve shirt with a blue undershirt, gray pants and black shoes. This outfit bears some resemblance to her S.T.A.R.S. uniform, she is not seen wearing a beret early in the game and later changes to a blue and black BSAA wetsuit, with black diving boots for her mission to the Queen Zenobia.

In Resident Evil 5, Jill wears her BSAA uniform in Revelations, with a blue cap as an addition. After being taken by Wesker, she is stripped of her uniform and fitted with a skin tight indigo blue and black battle suit. Her disguise over the battle suit in Kijuju includes a long cloak and a beak-shaped mask. Because of the experiments performed on Jill's body, a number of changes occurred: her exposure to the modified T-virus strain by Albert Wesker made her height increase to 5’8, as well as granting additional physical strength. Her time in cryostasis caused a pigmentation abnormality to her hair and skin, transforming Jill from a brunette into a pale blonde. An external device was embedded into Jill's chest to brainwash her into an obedient super soldier for Wesker and Excella. Once the device was removed, it left a scar in the center of her chest where it had once been attached (not shown in Mercenaries).

In the movie, Resident Evil: Death Island, Jill's hair is dyed brown as the roots and streaks of her natural pale blonde hair are remained and has a bob style like in her remake version. Her main outfit is a reminiscent of her appearance in the remake version of Resident Evil 3, her tank top is capri blue and now has white singlets, she was equipped with a dark blue shoulder gun holster, the waistline of her blue gray jeans are folded and unbuttoned while being tucked in from her tank top. The chest scar seen in Resident Evil 5 is not seen when she wears this outfit. When arriving at the island, she wears a white long jacket beneath her outfit."