Alex Mercer

While the virus itself can take anybody's form through consumption, in its typical form it looks identical to the deceased Gentek scientist Dr. Alexander J. Mercer due to the Blacklight Virus recreating Mercer's body down to the genetic level.

Appearance-wise, he is greatly identical to his human self albeit with paler skin tone due to Blacklight virus infection as well as having a sickly gray tinting around the eyes. The same goes to the latter's attire that he wore in his last moments along with plain blue jeans and black shoes; a button-up white shirt with a protruding collar kept partially buttoned, a plain gray hoodie, and a black leather jacket with a red interior, two horizontal white lines on each sleeve, and a loopy red winged insignia on the back. It must be noted however that said attire was Biomass-based construct and cannot be removed unless he shapeshifts since it was part of his very anatomy. Interesting though, that only the biomass mimics the clothing, which is organic matter, but Mercer will also consume the non-organic matter (for example metal and plastics) and he can use electronic equipment such as a walkie-talkie while disguised.

Perhaps as a result of his difficult childhood, Dr. Mercer is a callous, spiteful, and cold-blooded individual, both paranoid and borderline sociopathic. Most notably, just prior to his human death at Penn Station, he released the deadly Blacklight virus simply to spite those who denied him information. His motivations and plans are utterly personal and he rarely takes human cost into account, being able to murder scores of humans without remorse or hesitation. His intelligence was remarkable, though, commended even by McMullen; he was a "lateral thinker, with plans within plans."

The Prototype Alex Mercer inherited much of his human self's personality, most notably his sociopathic and paranoid side. As with Dr. Mercer, he rarely takes human cost into account as shown throughout his journey to learn about his true identity, being able to murder scores of humans without remorse or hesitation. The Prototype also inherited Dr. Mercer's deep emotional attachment towards Dana and Karen, leading him to seek their assistance in order to figure out what truly happened. Since Mercer believed himself and his creator Dr. Mercer are one in the same and even unknowingly behaved like the latter, neither of them suspected something off in him.

However, Mercer changed after discovering that he is in fact, an entity born from Blacklight virus-infected corpse of the real Dr. Mercer, and he had unknowingly masqueraded his creator since the day he awakened at the morgue, leading him developing an identity crisis. Putting that aside at first for the sake of stopping the first outbreak, it became apparent after the deed was done, since he didn't return to his human self's sister and opted to set out for soul-searching instead. At that point, he was uncertain whether he could fit in with humanity since he had stolen the identity of his creator.

Unfortunately, after repeated betrayals and mishaps during his time away from NYZ after the initial outbreak, Mercer's worldview became increasingly cynical and nihilistic. He decided that stopping the outbreak was a mistake and started a new one himself to usher in a new race; he claimed he was making a better world by doing so. In his new role as the leader of the Infected, Alex pursued his goal of spreading the virus in a far more active and aggressive manner than Elizabeth Greene ever did, even inserting spies within both Blackwatch and Gentek and using their resources and scientists to do so. Because he still retained his feelings for Dana, however, he opted to lock her instead when she turned against him. He was visibly hurt when Dana stated that "the Alex I knew died a long time ago", before eventually responded by said "I'm beyond life and death", leading her to realize her brother indeed gone on the day Blackwatch operatives executed him back then yet a surviving sliver of him became one with the virus who possessed his body and initially believed it to be its creator until discovering the truth.

Once reanimated by the Blacklight virus, every particle of Mercer's form, including his clothing and equipment, becomes comprised entirely of viral biomass. This substance can be manipulated at will. He can absorb the organic matter of other living creatures, converting it into more biomass. This process sustains and regenerates Mercer's health and is referred to as 'consuming'. In addition, Mercer can consume individuals, absorbing their knowledge, skills, and even their physical form, which he can call upon at will. He can manipulate his physical form to create weapons to attack his enemies, generate armor to defend himself, and take on the appearance of another person to disguise himself. During his battle against James Heller, he displayed the ability to consume multiple of his Evolved soldiers at the same time in order to power up his abilities.