Ada Wong is a woman shrouded in mystery, a beautiful but deadly professional spy. Not much is known of her past, but she was apparently working for an organization run by Wesker at the time of the Raccoon City incident. Wesker sent her into the city to retrieve a sample of the G-virus.

While on her mission, Ada came across a young police officer named Leon. At first Ada was trying to find ways to get around this pesky boy scout officer, but slowly began to develop feelings for him. Ada was shot at by Annette Birkin and it was Leon who took the bullet for her. Amazed that this stranger would risk his life for a woman he hardly knew, Ada began to fall in love with Leon.

She partnered with him as they went through the underground of Raccoon City, never letting him know who she really was. When Ada was attacked by William Birkin in a tram, she was heavily wounded and Leon took care of her. She professed her love for him knowing that soon she would have to betray him. That moment came when Leon obtained a G-virus sample and Ada held Leon at gunpoint, ordering that he give her the sample. Ada could not bring herself to pull the trigger when Leon refused to give up the sample, but at that moment Annette shot Ada in the back. Ada tumbled and fell into a deep chasm in the lab, but Leon reached out and grabbed her. While Leon struggled to pull her up, Ada asked for forgiveness and let go, falling into the abyss.

Ada's story did not end there, however. She survived the fall, and discovered that Leon was in the midst of a lethal battle with a Tyrant. She found a rocket launcher and tossed it to him while hiding in the shadows, allowing Leon to defeat the Tyrant. Ada then escaped the city before it was destroyed. The incident impacted her profoundly, however, and Ada left Raccoon City a changed woman.

Years later, Ada was recruited by a group called the Organization. She intercepted an email sent by scientist Luis Sera, detailing a cult that was using a parasite to take control of innocent people. The Organization sent Ada to retrieve the sample, as did Wesker, who assumed Ada was still loyal to him.

While on her mission, Ada found that her old love Leon was at the site as well. Ada remained in the shadows most of the time, guiding Leon without him even knowing it. She helped him kill Lord Saddler and took the sample from his grasp, this time keeping her duties in front of her emotions, escaping on a helicopter after giving Leon the means to escape the island. This helicopter was not headed for Wesker, however, as Ada sent Wesker a fake sample and kept the true sample for the Organization. Ada has double-crossed the most dangerous man in the world, and knows she will always be a target as long as Wesker lives. Yet it seems Ada is not too worried about being marked for life, as she remains as cool as ever, nothing like the emotional woman she left behind in Raccoon City.