*Alex Mercer, also known by his Blackwatch codename Zeus, is the playable protagonist of Prototype and the main antagonist of Prototype 2. He was the former head researcher of the Blacklight Project at Gentek. After learning that those affiliated with the project were being systematically murdered, Mercer attempted to flee the city with a sample of his research contained in a vial. Cornered at Pennsylvania Station, Mercer smashed the vial and unleashed the deadly virus into the surroundings. This triggered a viral outbreak that eventually covered all of Manhattan Island.

After waking up at a Gentek facility with no recollection of his past, Alex Mercer escaped the building, and soon discovered his new powers and abilities, granted by the virus he unleashed. He began to utilize his powers to learn more of his fragmented past, as he scoured all of New York for those responsible.

Alex Mercer came to life as the result of a vial of the Blacklight Virus assimilating into its creator, Dr. Alexander J. Mercer, its human host from whom he attained his identity. Dr. Mercer himself was the head of the Blacklight Project at Gentek in charge of engineering weaponized viruses from samples given to them by the government.

In the subsequent experimentations, the samples exhibited curious behavior, including mimicry and retention of genetic information from infected hosts. In time, Dr. Mercer and his team found themselves developing a particularly virulent and potent virus codenamed "Blacklight."*