One of the founders of Umbrella, he was the head of the Umbrella Training Facility located on the other side of Raccoon Forest. His deep compassion with leeches led to the creation of the T-Virus, made by combining the DNA of a leech with the Progenitor virus. Ozwell E. Spencer sent two of his subordinates, Albert Wesker and William Birkin, to assassinate Marcus and steal his his important research. Approximately a decade later, Marcus rises from the grave, with the help of his loving leeches, to seek revenge on Dr. Spencer for his betrayal. Marcus soon infects the Arklay Mountain Research Facility, which then sparks a chain of events causing the spread of the T-Virus, thus the beginning of the entire Resident Evil series.