Geo Mandrake was originally a scientist who worked for the Commonwealth Empire, but he defected in order to save his family, leading to him ending imprisoned. He is eventually rescued by the Resistance led by Bahamut, a former soldier of the Empire. After the Empire is destroyed, Mandrake starts working for the government, creating various weapons for the Contra forces as well as the cyborg Lucia.
After the end of the Alien Wars, the government forces obtain a sample of Alien Cell, which is then locked away in a vault. Mandrake starts growing resentment on the government for not allowing him to study the Alien Cell, eventually going insane and allying himself with Colonel Bahamut in order to carry on with his experiments.
Dr. Geo's Fate
His ultimate fate will vary depending on the player's choices on the game:
- If the player chooses to "Fight to the End" (regardless of the path taken on the second stage), the doctor will start fusing various monsters to attack the player, but the last fusion monster goes out of his control and eats him before attacking the player.
- If the player chooses to "Rescue the Research Lab" and "Surrender and Fight Later", Bahamut will betray him and implant the Alien Cell on him, turning him into a beetle/spider mutant which the player is then forced to fight.
- If the player chooses to "Chase Deadeye Joe" and "Surrender and Fight Later", he will appear in the blowing space station and turn the soldiers into mutants to stop the heroes. He will then confront the heroes on a bipedal walker while they take an elevator to reach Bahamut.
- Geo Mandrake is mentioned in Contra: Shattered Soldier. He is credited as the person who started the project on Lucia's original design.