(Capcom's primary storyline)
"There's nothing left to say. For you and I, Leon, we're merely different sides of the same coin..."
Jack Krauser (ジャック・クラウザー Jakku Kurauzā ) was an agent for the 3rd Organization during the War on Terror, and a supporter of Dr. Albert Wesker. Previously a soldier within USSOCOM known as "Silverdax,"  he was forced into retirement after a 2002 mission to South America with USSTRATCOM agent Leon S. Kennedy. During his employment within The Organization, Krauser took part in the infiltration of Los Iluminados to obtain a Plaga parasite. Krauser was killed in late 2004 by Ada Wong, who was on orders by her agency to steal the parasite.
Jack Krauser was an experienced soldier within the United States Army, having led many successful operations. During his days off, Krauser often participated in mercenary work, as he felt that he cannot function within normal society and thus believed that combat situations and being in the military is what gave his life meaning.
Operation Javier (2002)
"Something's wrong. It smells like... like a battlefield. Yeah... like 'death'."
— Krauser talking to Kennedy after entering the infected village
In 2002; before the destruction of the Russian branch of Umbrella, Krauser, a seasoned operative, (a member of the US SOCOM - U.S. Special Operations Command) was selected to be Leon S. Kennedy's partner due to the difficult nature of the operation.
He was sent to an undefined (Spanish-speaking) South American country situated within the Amazon rainforest, where he was to meet up with Kennedy by his means, choosing to pay a man to drive him to the rendezvous coordinates. Jack was unable to meet Kennedy by his initial choice of transportation due to a sudden riot taking place in a town along the route, leading to roadblocks being put in place. Not permitted to return fire on the riot police for their use of armed-violence against the individuals, Jack was forced to continue on his trek already ten minutes late. Faced with a large river obstructing his journey, Jack was lucky enough to hitch a ride on a freight train running nearby. Eventually, Jack met up with Kennedy at a nearby town along the train route; while Kennedy had made it there on-time, his tour-charted Cessna had been shot down along the way.
After meeting Kennedy, the two of them moved out through the rainforest to their mission, which was later revealed to be a Presidential order to limit the spread of the t-Virus and the selling of Bio-Organic Weapons. Their targets were Javier Hidalgo, a wealthy local drug lord, and an Umbrella researcher who was selling bio-weapons products to him.
Krauser and Kennedy have been sent on a mission by the U.S. government to infiltrate Javier's mansion in a small locale of Amparo. Finding Javier is their objective since he is a drug lord who has taken de facto control over a large area of jungle. He rules the entire area. The small government is unable to do anything about Javier's control of the drug trade, so Krauser and Kennedy have been called in.
The U.S. government has received information that a former Umbrella researcher has somehow entered the region. Sources indicate that something strange is going on, but no accurate information can be obtained. Unwilling to risk a biohazard incident, a secret military agency pairs Kennedy and Krauser and sends them into this volatile region to determine what, if anything, is going on.
Shortly after they arrive at their drop point zone (the Jungle), but before arriving at the village of Mixcoatl, Krauser tells Kennedy that he doesn't believe in B.O.W.s. Kennedy speculates that he sees the Enemy as being the same to him.
They found themselves having to cooperate as a two-person cell in a t-Virus outbreak. During their cooperation, he becomes more interested in Kennedy's experiences in the Raccoon City Destruction Incident. After learning as much from Kennedy as he can, he realizes that the enemy they are facing is entirely new to him, and thus starts to realize that B.O.W.s do indeed exist. Upon arriving within Mixcoatl, Kennedy and Krauser are faced by the zombified residence of the village, before finding their guide mortally wounded as well. They soon struggle past the various B.O.W's which they encountered, only to find a mysterious girl, named Manuela Hidalgo, along with a fierce amphibious B.O.W. which they soon manage to defeat for the time being.
Kennedy and Krauser are guided by Manuela through Javier's massive dam, only to encounter even more B.O.W.s. They then learn that the young girl is Javier's daughter, and had been infected with the Veronica virus, before being separated from her by Javier's men. As Kennedy and Krauser eventually struggled through the dam and met up with Manuela yet again, they learn that she was administered the virus to save her from a terminal illness which she and her mother contracted, with Manuela agreeing to take them to her father's mansion.
Along the way, Krauser, concerned about the possible transformations which Manuela could undergo due to the Veronica virus, learns of Kennedy being sent into this mission under the direct orders of the President, to eliminate the virus. Although Krauser agrees to help Kennedy, deep down he begins to feel jealous, almost spiteful, of Kennedy's elite status, as well as starting to doubt and reservations whether the US government brushed him aside, with him also desiring to complete the mission to prove his self-worth to the government.
As the two make their way through Javier's mansion, Krauser continues to contemplate the mission. He soon finds himself agreeing with Javier's mentality of "becoming stronger to survive," and he grows increasingly resentful of Kennedy. This leads Krauser to become obsessed with the power of the Veronica virus.
As the three make their way down to a warehouse, they find the truth about Manuela's control over the virus: She has her vital organs regularly transplanted from kidnapped girls to both reduce the pain of the virus and to keep her mind strong. Javier then sends out the same amphibious B.O.W. which Krauser and Kennedy encountered earlier, only to find that Manuela can keep it from attacking by singing.
As they try to protect her, Krauser ends up having his left arm impaled by the beast, severely wounding him, before he and Kennedy learn that the B.O.W. is Manuela's mother, Hilda.
As Javier merges with the Veronica Plant, becoming the "V Complex" bioweapon, Kennedy, Krauser, and Manuela work together to defeat it. All the while, Krauser becomes more and more convinced that the power of this virus is beneficial, and that destroying it would be a mistake. He thus becomes fully convinced that he must become stronger, viewing Kennedy as a "coward," and deciding that he will become more powerful.
After destroying Javier once and for all, Manuela is taken into the custody of the US Government. His arm does not fully recover, and he is thus taken out of commission from the US Military, further increasing his anger, before he would soon fall further into darkness. Because of this, he sought out Wesker, believing him to be the only one who will help him regain his strength and thus get back to work.
Los Iluminados incident (2004)
"You catch on quick, as expected. After all, you and I both know where we come from."
At some point in 2002, Krauser faked his death in an "accident" and sought out Wesker, to gain the power he desired so much after the incident in South America.
Krauser was sent by Wesker to the Ganados' island to infiltrate the cult group Los Iluminados and steal a Dominant species Plaga. Although Saddler did not trust him, he nevertheless gave Krauser a sample of the Dominant Species Plaga. The Iluminados hired Krauser to kidnap the president's daughter, Ashley Graham, promising him admission to Saddler's inner circle should he be successful. He would later become so enamored with the power of Plaga that he took the Dominant species Plaga sample he received from Saddler into his own body. The Plaga granted him physical agility and reflexes beyond that of an average human, as well as the ability to transform his arm into a large blade-like appendage that was durable enough to withstand even a direct hit from a rocket projectile, and because it was a Dominant species Plaga, Krauser retained his intelligence and free will (evidenced primarily by the fact that he was still loyal to Wesker, and not Saddler).[excerpt 1] Despite Krauser's success in kidnapping Ashley, Saddler still did not trust him, thus forcing him to call in Ada Wong as a result. However, Krauser continued to believe that Wong was untrustworthy and that she would betray Wesker, later warning her that he would kill her if she did. Wesker ordered Krauser to hunt down and assassinate Kennedy but failed due to Ada Wong's intervention, thus increasing his suspicions about her. During his fight with Kennedy, he also briefly let slip about him now being affiliated with Umbrella.
Hours later, he confronted Kennedy again in a large ruins area, telling him where Ashley was being held while also divulging the location of two of the insignias needed to bypass the gate. Kennedy quickly surmised that the third insignia was held by Krauser himself, with the latter answering in the affirmative. They then entered a long fight, with Krauser shooting a TMP, throwing flash grenades, engaging in hand-to-hand combat, and dispatching explosive robotic drones while Kennedy gathered the two missing insignias. As the fight was taking place, Krauser revealed his motives for restoring Umbrella: to restore order and balance to the world. After Kennedy retrieved the second insignia, Krauser confronted him on the roof of the tower, locking the doors behind him. C4 charges were set to 3 minutes while Krauser mutated his arm into a large bladed claw that was completely bulletproof and dealt a huge amount of damage. He used it to shield his upper torso, although his lower legs remained vulnerable to attack. Kennedy eventually managed to defeat Krauser, which resulted in his chest exploding.
Kennedy took the third insignia from Krauser's body and escaped the area before the charges detonated, with Kennedy also wondering what caused Krauser to go bad. After Kennedy and Wong met near the prison, she proceeded to the rooftops where she met Krauser, who had managed to survive. Although powerful, he was severely weakened from his previous encounter with Kennedy, allowing Wong to gain the upper hand easily. Krauser was finally killed once and for all, and true to his earlier suspicions, Wong would indeed betray Wesker shortly afterward.
Wong recovers the sample from Kennedy at gunpoint but does not send it to Wesker. Instead, she gives him a subordinate Plaga while sending the real sample to her superiors in the "Organization". However, Wesker still managed to recover a Dominant Species Plaga sample from Krauser's dead body, probably extracting tissue samples to grow his own.
- Koichi Hamamura, ed (2006) (in Japanese). biohazard4 kaitaishinsho revised edition. Famitsu. ISBN 4-7577-2638-4.
- Excerpt from biohazard4 kaitaishinsho, page 156:
"レオンのかつてのパートナーであり、 ナイフを使った格闘術のスペシャリスト。 みずから望んで寄生体を身に宿し、 超人的な身体能力を獲得している。 寄生体の力を解放すると、 その左腕が硬質なブレード状に変化 し、 すさまじい斬撃で敵を襲う。また、 このブレードは翼のように広げることで盾のかわりともなり、 ロケット弾の直撃にも耐えるほどの防御力を誇る。"
- Project Umbrella article: Inside Biohazard: The Darkside chronicles
- Project Umbrella article: BIOHAZARD Archives II
- Resident Evil: The Darkside Chronicles, Communication from Krauser 1
- Resident Evil: The Darkside Chronicles, Communication from Krauser 2
- Resident Evil: The Darkside Chronicles, Communication from Krauser 3
- Hamamura (ed). Kaitaishinsho. p.156
- Krauser's Note
- INSIDE OF BIOHAZARD THE DARKSIDE CHRONICLES, p.185: "ジャック・クラウザーによって持ち出されたプラーガのサンプルが、 彼の雇い主でアルバート・ウェスカーの手に渡る".