Appeared before Naked Snake during the 1964 Operation Snake Eater as a cooperative KGB spy sent by Soviet leader Khrushchev. Her mission was to supply him with information and acquire intelligence on the Shagohod.
She donned glasses and the alias Tatyana and approached Shagohod developer Sokolov. After Sokolov was captured by Colonel Volgin, she pretended to serve Volgin. After rendezvousing with Naked Snake, she uses both her identities as EVA and Tatyana to assist Snake on his infiltration mission and lead him to the massive fortress Groznyj Grad. There, after hearing The Boss's true intentions, she tells everything to Naked Snake in the form of a debriefing on The Boss.
EVA's true identity was a child of the Philosophers who remained in the People's Republic of China. Since childhood, she had received spy training in The Boss's Charm School, and eventually joined the Chinese People's Liberation Army General Staff Headquarters, Second Division. There, she learned techniques such as "bandit shooting," a horizontal sweep using the Chinese pistol. She took the place of the real EVA sent in by the KGB during Operation Snake Eater and attempted to steal the Philosophers' Legacy, a stockpile of three superpowers' capital, for China. She stole the microfilm containing the location of the Philosophers' Legacy that The Boss had recovered, and returned with it to China. That microfilm, however, had proved spurious, and the real article fell into the CIA's hands. Chased off by the Chinese government, EVA fled to Hanoi in the 1970s and disappeared.
Later, EVA met Big Boss again in Hanoi after he had left the FOX Unit. EVA joined the "Patriots" shortly thereafter. In 1972, as a part of the experimental Les Enfants Terribles Project that sought to create body cell clones of Big Boss, EVA participated as a surrogate mother for twins imbued with Big Boss's chromosomes. Those twins would grow up to become Solid and Liquid Snake. After learning of the Les Enfants Terribles Project, Big Boss left the Patriots. Eva, once more resonating with Big Boss, began to act on his behalf in secret while remaining with the organization.
She later fled to Eastern Europe, where she became Big Mama, leader of the anti-Patriots resistance, the Paradise Lost Army. In addition to taking in war orphans, she worked to stop Zero's ambitions and end the economy of war forever.