Ada

Ada was an artificial intelligence entity in prerelease concepts for Deus Ex. During the course of the game's development, Ada was cut and her role in the story was replaced by the Daedalus and Helios AI entities seen in the released game.

Development history
Ada was originally written to serve as the final antagonist of the game and would have featured in the moon base mission, which was to be the final mission of the game before the mission was cut. According to the Deus Ex Bible, the objective of the moon base mission was to stop Ada, which the Deus Ex Bible describes as "an AI that wanted to become 'benevolent' world dictator."

Ada was apparently based on Adam, an even earlier AI concept character in the Shooter: Majestic Revelations precursor concept. In Majestic Revelations, Adam was an AI entity who wish to control the world as a dictator, and the protagonist would eventually have to confront Adam on a space station named "Helios" where Adam's computer was held. These general plot concepts were seemingly retained when Adam was replaced by or rewritten as Ada, although the setting for the final mission of the game was moved from a space station to a moon base.

Later during the game's development, Ada was replaced by Daedalus and Helios. Meanwhile, the moon base mission was replaced by the Area 51 final mission. According to developer accounts, level designs for the moon base were later re-realized for Area 51.

A typographical error in Deus Ex design document v13.12 suggests that part of Ada's role was directly inherited by Daedalus. Specifically, this document contains the mistyped term "Daedelusmantly," which appears to have been the result of the use of a find-and-replace function to replace "Ada" with "Daedelus" (in this case, converting "Adamantly" to "Daedelusmantly"). Note that "Daedelus" (with an "e") was an early name for Daedalus.

Plot summary
Ada is mentioned in a single note in the Deus Ex Bible:

No explicit mention of Ada appears in other known documents. However, since many elements in Daedalus' backstory in prerelease documents heavily resemble that of Adam in the Majestic Revelations concept, it can be inferred that many other plot concepts for Adam were also carried over to Ada, before they were in turn carried over to Daedalus.