Nothing is known of Ada's background other than her Asian origin. Working in the shadows as a spy, she was present during the events that led to the destruction of Raccoon City, where she met Leon, in 1998. Their fates have been intertwined ever since, and they were reunited most recently in 2013 while investigating catacombs.
Ada is particularly fond of the color red, as can be seen from her tight-fitting red dress in RE2, her red halterneck Chinese-style dress in RE4, and her red shirt and scarf in RE6. In the RE4 minigame "Assignment: Ada," however, she wears black military attire from head to toe, and in The Umbrella Chronicles she is seen wrapped in a number of bandages, looking decidedly worse for wear, after being attacked by the Tyrant.