Alex Mercer

Alex Mercer is the villain protagonist of the video game, Prototype. He is also the main antagonist of the video game, Prototype 2

As a human
Once a human, Alex works for a company known as Gentek. He has no empathy, as evidenced when he is questioned of how does he feel of creating a deadly virus to be 10x deadlier, he replies that he "wasn't paid to feel".

One day, he is pursued by Blackwatch, a military unit and took a vial of the virus as "insurance". Alex is cornered by the team in Penn Station. As a result, he drops the vial to the ground, hoping it would kill the team. He is shot to death afterwards.

As a virus
His body is shown being bought to Gentek for dissection. the virus, having merged with his body, became an independent being based on Alex, codenamed Zeus. Zeus woke up, having no memory of how did he end up there, and tries to escape. Just then, Blackwatch corners him and shot him, but he survives.

Alex gets into contact with his younger sister, Dana Mercer, into helping him discover the truth. She even directed him to Karen Parker, his ex-girlfriend, to create a cure for the virus. However, the latter is possibly forced to work for Blackwatch as the genetic material he got for her is used to make a weapon against him. This is removed from him with help from Dr. Bradley Ragland.

Just then, Dana gets kidnapped by a Leader Hunter under orders of Elizabeth Greene. Alex has managed to locate her, and gets into a fight, but ended up creating the Supreme Hunter when he injected her with the same weapon. He saves Dana, nevertheless.

Next, Alex gets into contact with a mysterious informer, who knows everything about him. He reveals that he is the virus, and that Alex is just his role.

The contact lead him into a confrontation with Director Raymond McMullen, his ex-boss at Gentek, to get information. The latter reveals of how Alex Mercer is responsible for the plague by unleashing the virus in New York before having died at Penn Station.

Alex finally meets the contact, Captain Robert Cross, the specialist he fought early on. He reveals information on getting Colonel Taggert as a ticket to get into the Reagan to stop General Peter Randall from destroying Manhattan with a nuclear missile. When they got there, Alex absorbs Randall, and gets attacked by Cross, who is revealed to be the Supreme Hunter in disguise.

Alex defeats the monster, and puts the missile into the river. He fails to escape as the explosion takes him, too. However, his remains absorbed a crow, regenerating himself.

Prototype 2
Alex has witnessed a soldier named James Heller taking down the infected. What he didn't know is that he does that only to get revenge on Mercer for killing his family.

When Heller cofronts Alex, the latter infected him with the Blacklight Virus, giving him the powers he would have. This leads him to have a vendetta for Alex as he knows he is responsible for the death of his wife and daughter.

After Heller escapes the Gentek building, he is confronted by Mercer, who tells him that Blackwatch and Gentek are the ones responsible for the Second Outbreak, not him. After consuming a Blackwatch guard to verify this, Heller agrees to help Mercer with his plans.

After killing Dr. Anton Koenig, Heller is confronted by Mercer again, who tells him that there are more of "them" here, and explains to Heller that he is creating an army of "Evolved" to destroy Blackwatch and Gentek from the inside, along with the virus, and Koenig was one of them. Displeased, Alex tells him he should of killed him for that, but he will not, as Heller is far too valuable. After Mercer leaves, Heller finds out that Mercer intentionally creates the Second Outbreak, meaning he was the one who killed his wife and daughter, and begins sabotaging his plans along with another Evolved, Sabrina Galloway.

After Heller learns that Mercer has sabotaged the cure for the Blacklight Virus, Whitelight, turning them into Evolved, Heller heads to the Whitelight facility to dispose of the remaining barrels, but he is once again confronted by Mercer, who tells him that he is displeased that he was killikng his Evolved and ruining his plans, after which he tells Heller that he has no use for him anymore as he cannot tolerate his behavior to ruin him. He then trys to kill Heller, in a failed attempt. He then attacks the secret hiding place of Heller's contact, Father Luis Guerra, and kills him. Heller then meets Mercer's sister, Dana Mercer, who begins to help him on his quest to kill Alex.

After Heller learns that his daughter, Amaya, is still alive, he loses interest in Mercer and trys to save her. But when Heller arrived, Galloway, after being upset that Heller refused her offer to leave the city together, took his daughter to Mercer. Alex than took Dana and Amaya and locked them in a bank safe.

Death

 * "Huh. Welcome to the top of the food chain."
 * ―Alex's last word's to Heller before being consumed.

Heller finally faced Alex after the latter consumed his Evolved, including Galloway, to become stronger and faster. Alex used his blade, claws, whipfist and hammerfists against Heller. Alex was able to regenerate from the wounds caused by Heller, even mocking him. But after several hits, Alex attacked Heller once more, but Heller used his claw to slice off Alex's right arm. This injury was not enough and Alex formed the whipfist from his body to hit Heller.

Using the blade, Heller than sliced off the regenerated right arm whipfist from Alex. Weakened, Alex formed the hammerfists to smash Heller, but the latter used his Hammerfists to rip off both of Alex's arms. Defeated, Alex said to Heller, that he was now on the top of the food chain. After his last words, Alex was killed and consumed by Heller. Heller, having become extremely powerful from the consumption, uses a gigantic mass of tendrils to destroy all the infected citizens in the area, promptly saving Manhattan from the "Mercer" virus.

Personality
The original Alex was a monster with no empathy who ultimately unleashed the virus out of pure spite. On the top of that, he doesn't care about his younger sister, Dana, and is only using her as a pawn in his plans.

The virus creation that merged with him, Zeus, was ultimately a better creature, displaying acts of genuine heroism and was horrified and disgusted with the original's actions. Although 14 months later, his personality returned to his former self.