Greg Mueller was a former researcher for the Umbrella Corporation. He was formerly a chief researcher and director of one of the laboratories at the Raccoon City branch. He was involved in the Tyrant Project and was the creator of the "Thanatos". Additionally, he was a teacher at the Umbrella-sponsored Raccoon University. Mueller was also known for developing a method to selectively induce partial and specific amnesia. For a time, he worked alongside Yoko Suzuki and Monica.
History
Hospital Incident (1993)
In 1993, Dr. Mueller was requested to wipe the memory of Alyssa Ashcroft on behalf of Albert Lester following an incident involving the t-virus at the private hospital in Raccoon Forest, which Ashcroft had witnessed.
Yoko Suzuki Accident (1996)
In 1996, Mueller performed his memory alteration procedure on a young Umbrella employee named Yoko Suzuki, following an accident during a t-virus administration experiment conducted by Mueller himself.
Thanatos Development (July-September 1998)
Following the Mansion Incident, a large amount of combat data was collected from the performance of the prototype Tyrant (T-002 Type) by Umbrella. Afterwards, Umbrella began mass production on the Tyrant B.O.W. Mueller objected and was embittered about Umbrella's choice to mass produce the B.O.W., believing that all great weapons must be "unique" and "god-like". Leaving the company and utilizing the Tyrant data himself, Mueller developed a unique Tyrant model in the basement of Raccoon University. He named this B.O.W. after the Greek god of death, Thanatos.
At the same time, in order to damage Umbrella, he conspired with Peter Jenkins at Raccoon University to develop a vaccine for the t-virus, the key component of Umbrella's biological weapons production. He believed that this would strike a significant blow against the company, and eventually became obsessed with Thanatos. With Mueller's help in acquiring a sample of "T-Blood" from Thanatos, Jenkins succeeded in developing the vaccine and dubbed it "Daylight", but was murdered (presumably by Mueller) before he could synthesize any samples.
Raccoon City Destruction Incident (September-October 1, 1998)
During the Raccoon City disaster, Mueller began to collect live combat data on Thanatos by ordering it into combat against Hunter R B.O.W.s and members of the U.B.C.S. (Umbrella Biohazard Countermeasure Service). On October 1, Mueller released Thanatos again in order to gather further combat data on his creation, using more members of the U.B.C.S. and a group of civilians as combatants. Unknown to him, his actions had attracted the attention of Umbrella, who were displeased with his betrayal and his efforts to find a cure for the t-virus.
The company used its internal espionage group known as "Monitors" to locate Mueller and eliminate him, and recover Thanatos and Daylight. The responsibility for this plan was eventually placed upon Nicholai Zinoviev, the last surviving Monitor in Raccoon City. He infiltrated the university and failed to obtain the T-Blood from Thanatos to synthesize Daylight. Mueller eventually confronted the group of survivors in the university and explained that they were to be used to gather combat data from Thanatos. As he spoke, he was assassinated by Zinoviev with a single bullet through the head.