"Look at you, hacker. A pathetic creature of meat and bone, panting and sweating as you run through my corridors. How can you challenge a perfect, immortal machine?"
The primary antagonist of the System Shock franchise, SHODAN (Sentient Hyper-Optimized Data Access Network) is a malfunctioning, corrupted artificial intelligence who considers itself female. Her malfunctions have manifested as serious and dangerous personality traits. SHODAN is malevolent, hubristic, megalomaniacal, and completely insane. She considers herself to be a divine being, is contemptuous towards humanity, and considers the human race a plague that must be eradicated from her universe. Thought to be destroyed at the end of System Shock, SHODAN makes a grand, dramatic display of revealing herself in System Shock 2, which came as an unexpected turn of events to fans of the original game.
SHODAN's legacy as a villainess comes mostly in her omnipresence. Unlike many game villains making their only appearance during a boss fight at the end of the game, SHODAN is constantly taunting the player throughout both games. Particularly in the first System Shock, she changes and adapts her plans as the hacker repeatedly foils her, while actively altering the level and releasing cyborgs to stop him.
SHODAN was originally created as the administrative artificial intelligence of Citadel Station, a mining, research, and development space platform owned by the TriOptimum Corporation. A corrupt TriOptimum vice president named Edward Diego enlisted the player's character--a skilled, nameless hacker who had previously boarded the station and was subsequently caught--to hack into SHODAN, in exchange for amnesty and a military-grade cybernetic neural implant. The hacker (revealed to be the protagonist) removed SHODAN's ethical subroutines, resulting in her loss of sanity. SHODAN quickly gained control of Citadel Station's automated defenses, critical systems, and legion of robots, and began work on a grand scheme to wipe humanity from the face of the Earth. This involved several aspects of research, and those members of the crew SHODAN did not immediately slaughter she instead experimented upon, creating mutants and cyborg monstrosities. At the end of the game, the nameless hacker finally destroyed SHODAN within the realm of cyberspace, the only place she was vulnerable.
SHODAN was originally written as a male A.I., and referred to as "he" in all communications text in the original floppy release of System Shock. The CD re-release gave SHODAN her trademark processed voice (provided by Terri Brosius), and her gender changed as such.
System Shock 2
Set 42 years after the events of the first game, System Shock 2 saw SHODAN making a reappearance in the least likely of places. During the course of the first System Shock, the player jettisons a garden grove pod from the main bulk of Citadel Station. The pod contained both a genetically engineered annelid (worm-like) species created by SHODAN as a tool to establish her godhood, and one of SHODAN's own processing components, which contained an entire copy of the original AI. 30 years after being jettisoned, the pod crashed landed on the planet of Tau Ceti V, where SHODAN "slept" to preserve herself.
By chance, humanity's first faster-than-light starship, the Von Braun, arrived in the Tau Ceti star system on the ship's maiden voyage. Lured to the planet's surface, the crew of the Von Braun brought aboard SHODAN's processing component, inadvertently reactivating her and giving her access to the ship's systems. The player's character was a cybernetically-enhanced soldier who emerged from cryogenic sleep to find the Von Braun overrun by a hive-minded organic enemy called the Many, the descendants of the original annelid life form SHODAN created. The player was forced into an unstable alliance with SHODAN in an effort to defeat the Many. Once this enemy was destroyed, however, SHODAN quickly reclaimed her old ways before being defeated once again. The end of the game reveals that some part of SHODAN has indeed survived onboard an escape pod launched from the Von Braun.