(Covers information from Anderson's universe)
Dr. James Marcus is an Umbrella scientist took credibility for creating the T-virus, which could revive dead cells while the real person who created it was Charles Ashford. He used the T-virus to save Alicia from progeria. later the virus was used to cure many diseases and led to it's mass-production. However, the side effect of the virus wasn't discovered and the first outbreak happened. It was quickly covered up. After the outbreak, James Marcus and Isaacs argued about continuing the production of the virus. James disagrees to mass-produce it. Dr. Marcus also created the antivirus of the t-virus in case the t-virus escapes. Wesker later killed Marcus under Dr. Isaacs orders.
Wesker later killed Marcus under Dr. Isaacs orders, due to disagreements on the subject of mass-producing the virus.