- "With his sights set on becoming a full-fledged Atlas Field Operative, Decker took a job in security to get his foot in the door. Decker's CO calls him a "highly motivated individual", which in Atlas talk means he's a royal pain in the ass. Competitive and driven, Decker's enthusiastic attitude has led to a few raised eyebrows during security briefings, several arguments on the firing range and a psych profile that may keep him from reaching his goals."
- — Biography
Not much is known about Decker's life before working at the Atlas Corporation. What is known is that he attempted to join the army, only to be rejected due to his failing of a drug test. He then set out to become a field operative in Atlas, and joined as a security guard at the Atlas Biogenesis Research and Development Facility to get started. His enthusiasm would often cause him trouble, pushing his goal further away. Unbeknownst to him, he, along with two other Atlas employees, Kahn and Lilith Swann, share a unique genetic feature, allowing them to maintain immunity against Atlas' Manticore virus, which reanimates dead bodies as mutant zombies. They have this feature in common with Sentinel Task Force soldier Oz, who was the first known infected patient captured by Atlas at New Baghdad, and was experimented on by Atlas secretly at the very facility they work at.
During one night, a zombie outbreak occurs, and Decker is called in to help the employees evacuate. However, he is then forced to run from the oncoming horde. He later arrives at a helicopter landing pad, along with Kahn, Lilith and Oz (who was brainwashed into believing he's a janitor working at the facility). The rescue Warbird is attacked by zombies, and crash-lands in front of them. Decker is then forced to cooperate with the other three in order to survive. In an attempt to escape, all four survivors retrieve their employee keycards, and use them to call in a second Warbird for extraction. However, as the Warbird approaches the facility, it is shot down by an oncoming orbital drop, leaving the four survivors stranded. They eventually make a last stand against the zombies, but are defeated. Atlas forces arrive and save them in the nick of time, transporting them to a facility located near a Burger Town restaurant.
- "We got the high ground, what's not to like?"
- — Decker in the Infection Outro
Sometime later, they recover and find themselves in the midst of another zombie infection. Not only do they have to fend off the undead, but they also have to rescue civilians trapped in the vicinity of Burger Town. The four survivors eventually find a way to activate the Burger Town mascot, Bubby, which either comes to life and aides them in battle, or just simply explodes. While doing this, they also unknowingly launch a missile. After, they are stopped on the roof of the Burger Town restaurant and are taken captive by Sentinal forces. Their leader, Lennox, points a pistol at them and claims one of the four must die. Oz is then executed in front of Decker and the other two. The trio are then taken to an Atlas aircraft carrier somewhere off the coast.
While on the ship, the team finds several diagrams depicting Oz as "Patient Zero", prompting Lennox to reveal to them about Oz's real past, and how he wound up in Kahn's facility, as well as why they were special to Atlas. They also discover some data tablets containing the journal of the ship's former captain. Having learned the truth about what happened, the team then decide to sink the ship by setting it to detonate. However, as they prepare for extraction, they encounter Oz, who has reanimated and become a zombie.
As the four escape from the burning remains of the ship, they discuss their next move. They all come to an agreement that Oz must be eliminated, and thus head to the Trident Retreat, where Oz went before them to exact his vengeance on Atlas. Upon arriving, the group is forced to perform a series of challenges, set by Oz, before being teleported into a digital recreation of his memory. They finally confront Oz, who mutates into a horrific monstrous form. After a long ensuing battle, Oz is killed. Lilith then takes it upon herself and uses a flamethrower to burn his mutated corpse, while swearing vengeance on Atlas for what they did to him.
In the aftermath of the incident, Decker is awarded with a Purple Heart and a Medal of Honor, and is enlisted into Sentinel as a full-fledged soldier, with the help of Lennox. Unbeknownst to him and the others, Atlas had already created a large amount of Oz clones, stored beneath the Trident facility.
- While Decker does not wear any gloves, he can be seen wearing gloves when he puts an Exoskeleton on. His third person model also lacks the gloves.