Deus Ex endings

There are three possible endings to Deus Ex. Which one in particular plays out depends on the actions taken by JC Denton (the player character) in the final location of the game, Area 51. The sequel, Deus Ex: Invisible War, establishes that all of the possible endings are at least partially canonical.

Merge with Helios (Helios' plan)
Summary: Merge with Helios, creating a hopefully benevolent cybernetic dictatorship.

Requirements: Deactivate the uplink locks, engage the primary router and proceed to merge with Helios.

Cutscene: JC Denton speaks with Helios, is convinced to merge with it, and proceeds to rule the earth as an omniscient, objective, absolute ruler."If there were no god, it would be necessary to invent him."

- Voltaire

A new dark age (Tracer Tong's plan)
Summary: Embrace Tracer Tong's plan to destroy global communications and start a new dark age without any of the burdens of a corrupt civilization.

Requirements: Cut the coolant flow to the antimatter reactors, disable the failsafe mechanisms, and activate them to initiate a meltdown event.

Cutscene: Area 51 is destroyed by the massive blasts, cutting world communication networks and destroying both Bob Page and Helios. This thrusts the world into a technological blackout, but also frees it from media control by the Illuminati."Yesterday we obeyed kings and bent our necks before emperors. But today we kneel only to truth..."

- Kahlil, Gibran

Illuminati rule (Morgan Everett's plan)
Summary: Kill Bob Page by destroying the four blue generators, and rule with Morgan Everett as one of the Illuminati.

Requirements: Neutralize the four blue fusion reactors and trigger the Infusion Control Switch.

Cutscene: JC Denton and Morgan Everett discuss plans for the future in a world where the Illuminati rules unopposed. This shows JC is at least complicit in their plans, if not actively collaborating with them."Better to reign in hell, than serve in heaven."

- Paradise Lost, John Milton

Canonical ending
According to the events of Deus Ex: Invisible War, all three endings are at least partially canonical. The official guide for Invisible War confirms that JC Denton performed the actions of all three endings: Nonetheless, JC's actions did not fully result in the intended consequences. Although JC did merge with the Helios AI, the merge was not fully successful, as JC fell into a coma-like state. Additionally, it is also stated in the guide that the Illuminati lost all means of controlling nations and peoples and that JC and Paul Denton were powerless to protect governments from warlords and from the damage already done by the MJ-12 shadow government, indicating that the Illuminati were unable to consolidate power following the destruction of Area 51. JC and Helios later formed ApostleCorp, which opposed the Illuminati, as seen in Invisible War.

The canonicity of all three endings was also confirmed by Invisible War 's game director Harvey Smith, who felt that the combination of endings was more interesting than any of the three endings alone.

Invisible War also establishes that JC's destruction of the telecommunications infrastructure resulted in the Collapse. However, communication and globalization were eventually able to return, as seen in Invisible War.

Trivia

 * In an hour-long narrated playthrough of Deus Ex with Sheldon Pacotti and Chris Norden, Warren Spector noted how he originally wanted a fourth ending to be possible in the game. This fourth ending would allow JC to side with Bob Page and Majestic-12, presumably letting Page merge with Helios and killing Everett. This is mentioned around 49:20 in the YouTube video.
 * Some evidence of this ending still persists in the final game, with Page at one point pleading with JC by offering him total control of Europe (this would apparently have been a serious option had the last ending been included). This corroborates some rumors which have circulated since the game's development, which suggest that originally Deus Ex would have included a second "MJ12 Loyalist" path to completion, which was later scrapped. The reason for the omission of this fourth ending is as of yet unknown.