Ada Wong is the pseudonym of a Chinese-American spy and mercenary who recurs as an antiheroine in Capcom's survival horror video game series Resident Evil.Her real name and background before working in espionage remain unknown. Introduced as a supporting character in Resident Evil 2 (1998), Ada is hired by an unnamed organization to steal the G-virus mutagen developed by the Umbrella Corporation, a pharmaceutical company responsible for a zombie outbreak in the fictional American metropolitan area of Raccoon City. Ada meets and allies with rookie police officer Leon S. Kennedy to access Umbrella's underground biological warfare laboratory, where she is outed as a mercenary by scientist Annette Birkin. Despite being severely wounded, Ada helps Leon destroy the T-103 Tyrant and escapes from Raccoon City before its destruction by a nuclear strike as part of a U.S. government cover-up.

Ada returns in Resident Evil 4 (2005). She is sent to a rural Spanish village by Albert Wesker to retrieve a sample of the mind-controlling "Las Plagas" parasite from the Los Iluminados cult. During her mission, Ada encounters Leon as he attempts to rescue the U.S. president's daughter, Ashley Graham, who has been abducted by the cult. After helping Leon kill the cult's leader, Osmund Saddler, Ada steals the sample from Leon and makes her escape in a helicopter. On the helicopter, Wong contacts Wesker and demands to know his intention with the sample. Wesker reveals his intention to expedite change, in which a hundred will give their lives so that one may live. Hearing the insanity of his ambitious plans, Wong holds the pilot at gunpoint and orders him to change their course and make off with the sample. Later ports of Resident Evil 4, beginning with the PlayStation 2 version, include a new scenario featuring Ada as the playable character. Entitled "Separate Ways", it depicts the events of the main game from her perspective and highlights her relationship with Leon.