(Covers information from Anderson's universe)
This was a clone of Doctor Alexander Isaacs who took on a leading role in the Umbrella Corporation late in the Global T-Virus pandemic. Like the real Dr. Isaacs, he is a religious fanatic who wants to cleanse the earth of people and start anew with the Umbrella employees, and is unaware of his identity as a clone. He is portrayed by Scottish actor Iain Glen.
As the extinction of humanity during the Global T-Virus pandemic fails to go according to plan, the Umbrella Corporation creates this clone of the real Doctor Alexander Isaacs to lead the effort to finish "cleansing" the world of humanity. This clone believes himself to be the real Isaacs, awoken early from stasis to finish the cleansing of humanity. During this effort, Isaacs encounters and kills several Alice clones who oppose his plans, cutting off their heads and storing them in a drawer in his tank as trophies. Over time, this Isaacs comes to believe that he is the holy instrument of God sent to cleanse the world of humanity and transforms into an insane religious zealot, something even the real Isaacs wasn't.
Encounter with Alice
In order to destroy the last human settlements, Isaacs personally sets out with three Undead armies led by Umbrella tanks to the ruins Raccoon City where one of the settlements is located in a tower. Inside of his tank, Isaacs keeps several prisoners who he attempts to indoctrinate to his fanatically religious views and who are terrified of him.
Along the way, Isaacs and his men encounter and capture Alice who had been rendered unconscious after attempting to steal an Umbrella motorcycle. Alice is shocked to see Isaacs, having believed him dead some time before. Alice quickly realizes that the Isaacs she killed was simply a clone and comes to believe that this was the real Isaacs. From Alice's comments, Isaacs realizes that she knows of the anti-virus and decides to force Alice to run behind his tank to force her to talk.
After a while, Isaacs learns that Alice has disappeared and sends his men on top of the tank to locate her. When Alice begins fighting his men, Isaacs climbs on top of the tank to battle Alice himself, proving to be a match for her. Alice eventually forces Isaacs to release her bindings, but he gains the upper hand in the fight. Spotting a motorcycle in a side compartment of the tank, Alice opens it, amusing Isaacs who knows she can't escape as she is not an authorized user of the motorcycle. In response, Alice cuts off Isaacs' hand and uses it to activate the motorcycle and escape. Isaacs' hand is then dropped to the ground where it is eaten by an Undead. Isaacs, in great pain, enters the tank where he has his men attempt to kill Alice with the tank's weapons, but they fail and she escapes. Isaacs' stump is bandaged and he warns Albert Wesker of the events.
Attack on the settlement
Isaacs' army eventually reaches the human settlement in Raccoon City where he prepares to attack. To Isaacs' anger, his second tank is destroyed by a makeshift bomb made out of a gasoline barrel. Isaacs then orders the "bait" released and sends out one of the prisoners from his tank, chased by the Undead from his army. Isaacs watches as the woman races towards the front gate of the settlement with Claire Redfield and Doc desperately trying to save her while Alice drops another bomb on the Undead. When the woman is nearly at the gate, Isaacs has his men kill her with the tank's weapons and then blow open the gate. Isaacs watches in glee as the settlement's defenses are overrun by his Undead army. However, to his shock, Alice kills most of the Undead army by pouring waterfalls of ignited gasoline on them from the roof.
After killing most of Isaacs' army, Alice climbs onto his tank and pours gasoline inside. Realizing what's about to happen, Isaacs orders his men to close the vents, but too late as Alice ignites the gasoline with a flare. The ignited gasoline kills the tank crew, but Isaacs manages to escape out the back through the prisoner compartment. He then hides nearby and listens in as Alice discusses a mission into the Hive to get the anti-virus.
Leading an army
Desperate to stop Alice, Isaacs meets up with one of the other two Undead armies heading to the human settlement and tries to redirect it to defend the Hive. When the tank crew refuses, Isaacs murders them and takes control of the tank for himself. Isaacs leads the Undead army to the crater in Raccoon City, but loses control and crashes the tank at the bottom. Drawing the army's attention, Isaacs jumps from the tank and leads them on a charge towards the Hive.
Encounter with himself and death
Reaching the entrance to the Hive, Isaacs is shocked to find Alice with the real Doctor Alexander Isaacs. The Isaacs clone, created to believe that he is the original as all Umbrella clones are created to do, refuses to believe his original self's insistence that he is the clone. Enraged, the Isaacs clone attacks the original and stabs him multiple times, causing the original Isaacs life support system to fail, killing him. Pleased, the clone repeats that he is the real one to Alice before being attacked and killed by the Undead led by an Undead Commander Chu. Thanks to the clone's attack, Alice is able to release the anti-virus which kills the Undead army, including the ones attacking the Isaacs clone.
Having been created with all of the memories and knowledge of the original Alexander Isaacs and thus the original's personality, this clone possessed the same ruthless, sadistic, psychopathic nature as the original. However, due to his differing experiences following his creation, the clone appeared to have become even more ruthless and sadistic than the original, showing great joy in torturing prisoners in his tank just because they "sinned" and keeping the decapitated heads of Alice clones he killed as trophies in his tank. The Isaacs clone shows no regard for his own men, appearing to see them just as a means to an end and going so far as to murder an entire tank crew that disagreed with his orders as they had received conflicting orders from Albert Wesker.
Like the original Isaacs he was cloned from, the Isaacs clone possessed a deep religious belief. However, the beliefs of the clone extended much farther than the original's ever did. This Isaacs clone came to see himself as the holy instrument of God in wiping the world clean of humanity and adorned his tank with crosses, wore one around his neck and often quoted the Bible. Rather than being a religious fanatic like the original Isaacs, the clone's experiences while hunting down the remainder of humanity appeared to have transformed him into an insane zealot willing to use himself as bait for an Undead army just to complete his "holy mission."
Like all of the Umbrella clones, the Isaacs clone was programed with the belief that he was the original. However, due to the clone's insane nature, his reaction to being confronted with the real Isaacs differed from how a normal person or clone would react. The clone's denial was so strong that he attacked and killed the original Isaacs calling the original a liar and an abomination. His attack appeared to have been solely motivated by the belief that he was the original and that anyone who claimed differently was an abomination who deserved death. After killing the original Isaacs, the clone appeared to be more interested in asserting his belief that he was the original to Alice rather than stopping her or paying attention to his surroundings, leading to his ultimate downfall.
Ultimately, while starting as an exact copy of the original Alexander Isaacs, the Isaacs clone's experiences in the world following the start of the Global T-Virus pandemic appear to have driven him insane and transformed the clone into a much more extreme version of the original Isaacs.
- Unlike J. Isaacs, this one truly believed himself to be Doctor Isaacs. The other appeared to serve a similar role to "Bad Rain" and the clones of Carlos Olivera and James Shade: the clone of a real person who was assigned to the task of an employee with no knowledge of their true nature or identity.
- The reaction of the tank commander of the second Undead army to his orders indicates that this clone may not have been as in charge of Umbrella as he believed or that Wesker was able to countermand his orders since the real Isaacs was being woken up.
- In an ironic twist, the original Isaacs found the fact that the clones believed they were the original highly amusing with that belief in this clone leading to the original's death at the clone's hands.
- In the novelization of The Final Chapter, the clone developed an infection from his cut-off hand, resulting in a fever that only increased his deranged state of mind. In the movie, it is unclear if the clone develops an infection from the wound or not though he does appear to be more sweaty and pale afterwards. He is also described as having several bites when he appears at the end with the Undead army, causing Alice to realize the clone used himself as bait to lure them to the Hive. In the movie, he does not appear to have any bites at this point.