In 2002, Jack Krauser is on assignment with special operative Leon S. Kennedy. The duo have been assigned to capture a drug lord named Javier Hidalgo. Upon arriving, they notice that the streets are deserted and they overhear a news report about missing girls. The duo notice a villager approaching them and Leon becomes suspicious. The villager is infected with the T-Virus and attacks Krauser. The dead immediately make their presence known and Leon and Krauser fight their way to the meeting spot with their guide. Unfortunately, their guide is on the verge of death. He states that the villagers rescued a girl that had fled Javier's mansion and that she was responsible for the fate that had befallen the village. While Leon and Krauser are discussing the situation, their guide is dragged away through a hole in the floor boards.
Making their way to the church so that they can take the boat to the dam, Leon and Krauser find the only other living person in the village, a girl named Manuela. Manuela is singing and as soon as she stops, the trio come under attack from a large B.O.W. The beast is amphibious and it is not until Leon and Krauser bring the church bell down on its head that it is defeated.
Manuela agrees to take Leon and Krauser to Javier's Mansion, despite the fact that she just ran away from there. When the trio reach the dam, they come face-to-face with Javier who explains that he has been frantically searching for his daughter. Despite the daughter obviously being Manuela, Leon and Krauser are baffled at this news, as there was no mention of a daughter in their briefing. Also, Javier reveals that Manuela has been subjected to the T-Veronica Virus. Leon and Krauser fall into Javier's booby trap and are sucked into the dam's water way. Manuela jumps in after them to escape her father.
Leon and Krauser discuss the situation and revelations and Leon reveals that he is under special orders from to President of the United States to destroy all traces of the T-Veronica Virus. Krauser agrees to follow Leon and the two eventually meet up with Manuela. At the mansion, it is revealed that Manuela needs fresh human organs for 15 years to repress the Veronica Virus and that Javier is responsible for the missing girls throughout the region. Manuela had run away after forcing her doctors to explain how she had survived a disease that had taken her mothers life so much faster and that there was no cure for. Upon learning of the girls who had been murdered to keep her alive, she fled and her father infected the doctors and their guards as punishment. Prior to their showdown with Javier, Krauser is stabbed in his left arm by a bio-weapon from one of the B.O.W.'s., referencing the unrelated mutation he would later gain in that limb, but recovers.
Javier has also exposed himself to the Veronica Virus and mutates into a giant monster. The virus begins consuming his entire body and Manuela uses her blood to help Leon and Krauser defeat her father. Kennedy and Krauser (and Manuela, if the players' actions allow her to survive) are then extracted from the region to safety (and Manuela is placed in government protection).
Sometime after this mission, Krauser fakes his death and joins Wesker's organization.
His Role in Resident Evil 4
In Resident Evil 4, Krauser, infected with a powerful Master breed of Las Plagas, is first seen being ordered by Osmund Saddler to kill Leon Kennedy. Krauser's real reasons to be on the Ganados' Island is to infiltrate Saddler's organization Los Illuminados to get a Master Plaga sample and bring it back to his true employer, Albert Wesker. Krauser is working alongside Ada Wong, but they don't get along at all because Krauser believes Ada is untrustworthy and will betray Wesker. Krauser fails to assassinate Leon when Ada saves Leon from being stabbed by Krauser's blade, rightfully increasing his paranoia towards her.
Krauser isn't seen for a while until he ambushes Leon, leading to a gun fight between the two. After playing a little game of hide and seek with Krauser, they finally find themselves at the top of a tower in the area. Krauser then demonstrates the Plagas-borne ability he has to mutate his left arm into a huge bladed weapon which he uses as an attacking weapon, and a shield from bullet fire. Leon is eventually able to subdue Krauser and escape the area before Krauser's laid explosives blow up.
Krauser then appears at the end of Assignment Ada, being the final boss. The fight is basically the same as Leon and Krauser's last fight while he has his blade, except the area is a narrow bridge with much less running space. At the end of the mini-game "Seperate Ways," Ada and Krauser have another encounter. Krauser appears to have wounds from the explosion but lives. He appears to be eliminated by Ada, but there's no concrete proof that he's dead. On Krauser's Mercenaries screen, it shows him looking at an explosion on a boat, which could mean that he's still alive.
Jack Krauser is available for play in the Resident Evil 4 mini-game "Mercenaries". To play as Krauser, you first must get a 4 star rating on Salazar's Castle level. In the game, Krauser is one of the more powerful playable characters. He has his bow and arrow and knife as default weapons. He starts with a few flash grenades and a first aid spray. His arrows have as much power as the shotgun, though much more harder to aim with at times. The most interesting thing about Krauser's character is that he has the use of his mutated arm. When you've killed enough enemies, Krauser's left arm will glow red. After pressing a certain button combo his arm will full mutate and it can only make a straight dash from his fixed location, but it will kill anything in the path of the dash length. That move is very helpful when having to deal with the stage bosses.