Carlos' character is based on the character of Carlos Oliveira from the Resident Evil 3: Nemesis video game, who is also a disgruntled Umbrella mercenary.
Carlos and his UBCF unit were dispatched to Raccoon City following the outbreak of the T-virus. The team's orders were to find and secure any remaining corporate assets before the city was completely destroyed. After witnessing a woman cornered on a rooftop by Undead, Carlos abandoned his orders and commanded his team to land. While Carlos killed the Undead attacking the civilian, she had already been bitten and chose to commit suicide rather than turn into one of them.
Carlos and his team later engaged in a fierce ground war against the Undead alongside the remaining Raccoon police forces, but eventually they were overrun and only Carlos and his fellow soldier Nicholai escaped. Carlos had become infected after one of his men turned into an Undead and bit him on the arm, but he wasn't yet ready to give up. As fortune would have it, Umbrella scientist Dr. Ashford was using the city's phone network to recruit survivors to find his daughter Angela, and so Carlos and Nicholai headed to the school where she was hiding and their they encountered Alice and Jill Valentine, who had found Angela. Although Nicholai was killed by infected dogs, Carlos was cured of his infection by receiving an injection of anti-virus that Angela had been carrying around in her lunchbox.
Carlos joined Alice and the others as they made their escape from Raccoon City on a stolen Umbrella chopper and went into hiding with Jill after Umbrella put out a warrant for their arrest when the pair tried exposing the corporation's involvement in the destruction of Raccoon. While Terri Morales' tape had been discredited, Alice was still alive and in Umbrella's custody, so Carlos, Jill and L.J. Wayne infiltrated the company's San Francisco branch to rescue her. Alice was released, but no one knew what Umbrella had done to her.
Five years after Raccoon City, the Earth has been devastated by a global T-virus pandemic. During that time, Carlos has joined Claire Redfield's convoy travelling across the Nevada Desert, offering his geurilla expertise to help the survivors defend themselves from the many perils of the new world. Apparently in the early days of the plague, Carlos and Alice parted ways since Alice was being tracked by Umbrella and didn't want to endanger anyone else.
After Alice meets up with the convoy, she, Carlos and Claire agree to head toward Alaska to find Arcadia, a supposed safe haven free of the infection. The convoy later arrives in the half-buried ruins of Las Vegas to refuel and resupply, only to be attacked by Umbrella's latest creations: a pack of Super Undead that have been enhanced after failed domestication attempts made them more aggressive. During the battle, L.J. - who had been bitten on the chest by an Undead earlier in the film - succumbs to infection and bites Carlos on the arm before being put down.
The convoy pursue an Umbrella chopper back to its base which is surrounded by the Undead, and Carlos comes up with a plan to get the rest of the survivors inside so they can steal the chopper. Since he is infected, Carlos has little time to live and so he sacrifices himself to save the others. He drives the convoy's tanker loaded with explosives toward the Umbrella base, running down many Undead before overturning the truck just before it hits the fence surrounding the entrance. As dozens of Undead clamber over the crashed tanker, Carlos finds a last spliff left by L.J. and lights it up. He lights the fuses on the explosives and then the truck violently detonates, vaporising Carlos and blasting all of the Undead surrounding the truck, giving Alice and the other survivors an opening to get to the Umbrella chopper.
Two clones of Carlos appear in the fifth Resident Evil film. One clone - named Todd - is a test specimen inside the Umbrella Prime facility, living in the Suburbia test bed. He appears to be married to Alice and they have a deaf child called Becky, but of course this Alice and the little girl are also clones. During a test procedure, Todd is bitten and infected by a mutated Undead. He later turns into one and feeds on his "wife".
Another clone of Carlos appears as a member of an Umbrella security squad led by the brainwashed Jill Valentine. This clone dies when Umbrella Prime is flooded, crushed and drowned by tonnes of freezing Arctic water.