Eva is initially introduced as a former NSA agent now American defector and KGB agent sent to help Naked Snake during operation Snake Eater, she is said to have defected with a man named ADAM. First appearing in Metal Gear Solid 3: Snake Eater she is a female fatal attraction spy in the service of the Chinese branch of the Philosophers set to retrieve the Philosopher's Legacy, having grown up in an school run by the Chinese branch of the Philosophers who trained her to infiltrate the West.
During Operation Snake Eater, she is ordered to help Naked Snake, who is on a mission to rescue Sokolov, a Soviet rocket scientist who failed in his bid to enter America and is now being forced into developing an advanced nuclear equipped tank (The Shagohod). Her true purpose is to obtain the Philosophers Legacy a huge stockpile of funds that China, Russia and The United States amassed during the First World War while the American's and Russians are preoccupied by Colonel Volgin's use of the Davie Crockett. She also disguises herself as Tatyanna first as Sokolov's lover and later Volgin's. Eva also displays great skill on a motorbike at several points during the mission a skill she demonstrates again 50 years later with Solid Snake. After the operation she is presumed dead but then reappears in Metal Gear Solid: Portable Ops. After this she joins the newly formed Patriots because of her devotion to the late Boss's desire for a united world. After the rift between Zero and Big Boss starts to form she agrees to carry his children when he is in a coma so his legacy could be continued through the "Les Enfants Terribles" project. However she is only the surrogate mother of the twins as another Japanese woman's genetic data was used to create the children.
Eva also makes an appearance in Metal Gear Solid 4: Guns of the Patriots where she is known as Big Mama. She appears in the European portion of the game and is revealed to be working with Raiden and other war orphans to protect them from the system setup by the Patriots. She is killed because of the Patriots use of a new strain of Foxdie designed to kill all the original Patriots now working against Zero and his A.I.'s and using Snake as a vector much like the Shadow Moses incident.
Her sizes are 35 - 26 - 34