Dr. Isaac was a medical doctor at the Raccoon General Hospital. Like almost all personnel at RGH, he died during the Raccoon City Destruction Incident as the injured and infected flooded into the hospital for treatment before ultimately turning and killing the staff. He later reanimated, himself, and attacked the survivors as they searched the hospital for supplies.
He is unlocked by beating The Hive scenario on Normal difficulty and costs 6,000 points. He has a Hemostat in his inventory. He can be unlocked in File #2 and purchased for a cheaper price by using the Data Convert option. He is a George-type character.
There is a second version of him used for Zombies that can only be used with cheating devices. This version lacks proper stats, resulting in being unable to damage enemies and running very slow. The only way to fix this is to use stat modifier cheating device codes.