"The right to be a God... That right is now mine."
A product of the Umbrella Corporation, Albert Wesker was the standout member in the Wesker children project. He spent many years as part of the Umbrella team, before transferring to the S.T.A.R.S. division of the Raccoon City Police Department. As Umbrella began experimenting on animals and people, Wesker began to lay out plans for his own rise to power.
During the Mansion Incident, Wesker duped his S.T.A.R.S. team into believing he was their ally and commanding officer. Faced with the mutated plants and animals that infested the mansion, all but a few of the team members died. While Chris Redfield and Jill Valentine stopped the Tyrant, Wesker led them to believe he had been killed by it. In reality, Wesker had injected himself with a chemical provided to him by former colleague William Birkin, and his body was resurrected, now with superhuman abilities.
Years later, Wesker sent Ada Wong into a remote region of Europe to retrieve Plagas samples. Ada crossed paths with Leon S. Kennedy a number of times, and though Wesker was likely aware of the aid she provided Leon, did nothing to interfere. He was prepared, however, for Chris Redfield to come looking for him following the Kennedy report that Leon followed after his eradication of the Los Illuminados.
Wesker then travelled to the estate of Ozwell E Spencer, who revealed to Wesker that he had been the one in charge of all the experimentation and bio-organic weapons. Spencer had hoped to use these to force the next phase of human evolution, but with both the Plagas and the Progenitor Virus at his disposal, Wesker informed Spencer that he would assume that role and shape the world to his own ends. As Wesker killed Spencer, Chris and Jill entered the room and engaged him in combat. Despite their skill with firearms, the duo could not compete with Wesker's inhuman physical strength and speed. Wesker leapt from the window, taking Jill with him. This led Chris to believe her dead, when in reality Wesker had taken her prisoner, attached a control device to her chest, and commanded her as one of his underlings.
Eventually Chris and Wesker met again in the Kijuju region of Africa, where he and his new partner Sheva Alomar took on wave after wave of Plagas-infected Majini and wildlife. These proved stronger than those Leon had encountered five years earlier, but the two manage to track down Wesker through Ricardo Irving and Excella Gionne. Wesker revealed to them his plans to unleash Uroboros worldwide by spreading it into the atmosphere, as well as the fact that Jill was still very much alive, albeit under his control. Chris and Sheva struggled to free Jill, but eventually succeeded. Afterwards, Chris and Sheva followed Wesker to his jet, fighting him in mid-flight until the aircraft crashed into a volcano. Furious with the duo for having foiled that which he had waited so long for, Wesker unleashed his own mutated form. While he nearly killed Chris and Sheva, he was forced into the lava and blown up by an RPG round as Jill and Josh Stone came to the rescue.
Throughout all the Resident Evil games, Wesker carried himself with a cool confidence. Despite the fact that much of his achievements were met through manipulation and murder, he did have a hand in much of the research he ended up taking for his own use. His idea that humans needed to be saved through a forced evolution into something monstrous and controllable, as well as he desire to be akin to a God shows his delusional mindset. And it is because of this that he shows little to no restraint in just how evil he can be.