James Marcus is one of the three founders of the Umbrella Corporation and the creator of the T-Virus. He was killed by Albert Wesker and William Birkin under the orders of Ozwell E. Spencer (one of the co-founders of the Umbrella Corporation). The T-Virus brought Marcus back to life and seeking revenge, he unleashed the T-Virus infection in the Arklay Mountains research facility. This incident started the events of Resident Evil 0 and Resident Evil 1.
Discovery of the Progenitor Virus
James Marcus was an expert in Virology and in school he befriended Edward Ashford and the two began the creation of the Progenitor Virus. The two needed funds in order to continue their experiments, so Ozwell E. Spencer was added into the mix. Backed by the fundings provided by Spencer the three discovered the Progenitor Virus in 1967.
Marcus and Spencer wanted to use the virus as a weapon while Ashford wished to research it. To hide the illegal experiments they were conducting they developed Umbrella, a pharmaceutical company secretly a biological weapons business. In 1968, Marcus was made the General Manager and Research & Development Director as well as becoming head of the Arklay Mountain Research Facility.
In 1978, Marcus created the T-Virus by mixing the Progenitor Virus with leech DNA. Due to this discovery, Marcus became respected by all his colleagues and researchers but made Spencer completely paranoid. Marcus soon after took Albert Wesker and William Birkin before Spencer shut down the facility. Marcus lived in isolation continuing his work on the T-Virus. During this time he created the Lurker, Eliminator and the Plague Crawler. As time progressed Marcus' mental state was getting worse and worse and he began using his assistants as guinea pigs until he was the only one left.
Spencer's suspicions had reached it's peak and he ordered Birkin and Wesker to assassinate Marcus in 1988. When Marcus was killed one of his leeches crawled into his mouth and their DNA bonded. Over the years, Marcus gained control over the leeches, whole also taking on a younger version of himself.
He stayed in the facility with the goal to exact revenge on Umbrella but was later killed by Billy Cohen and Rebecca Chambers a day before the Mansion Incident.