Warden

The Warden or the Warden Servitor is a heavily modified Fallen Servitor that was used by Variks, the Loyal to monitor the Prison of Elders in Destiny. Its core machinery has been removed, leaving a hollow shell affixed with multiple devices and parts of unknown purpose. With its core gone, the Warden appears to lack the sentience of a standard Servitor, instead having been replaced with an AI copy of Variks. This AI runs the gauntlet that Guardians can participate, informing them of the prisoners they are about to battle and directing them to the proper chamber of the prison.

After the massive Scorn prison break and Variks's disappearance, the Warden began malfunctioning (likely from the Trickster's works). With its programming stuck on the Challenge of the Elders, its erratic behavior drove what remained of the Prison into further chaos before it was destroyed by a Guardian fireteam, supported by the Drifter whom owed a favor to The Spider.

Gameplay
The Mad Warden enters the arena after defeating the enemies that were fighting each other in it. Contrarily to other Servitors, its ranged attack is a continuous Solar beam, dealing high damage. Every quarter or so of its health, it will teleport to one side of the arena, calling in Cabal and Vex to fight, and releasing a highly damaging solar wave for a few seconds, that can only be avoided by taking cover in the shadow of pillars or rubble. In its last quarter of health, it will summon Zhagal, Disgraced Colossus and Edyx, Exothermic Mind alongside their respective races to aid him in the fight. All that said, the Mad Warden doesn't have health gates, and can be killed before he can do anything with concentrated damage on any difficulty lower than Legend.

Trivia

 * The Servitor core found in the Vestian Outpost may be the same one that was extracted from the Warden.
 * Although the Warden first appeared in the House of Wolves expansion, it did not have an official name until The Taken King's Festival of the Lost event, which included a mask bearing the Warden's likeness.
 * Though dialogue between The Drifter and The Ghost seems to indicate that Variks and the Warden were in a symbiotic relationship, the precise nature of the link remains unknown.
 * Aside from the Techeuns, The Warden is so far the only character in the franchise that has gone from an ally to an enemy.
 * The Warden is also the only ally that has fought The Guardian outside of the Crucible and Gambit.
 * In Season of the Worthy, there was an issue where, for the purposes of Strike bounties, the Warden was not counted as a Fallen boss in Warden of Nothing.
 * Instead, it seemed to count as a Vex boss.

List of appearances

 * Destiny
 * House of Wolves
 * April Update
 * Destiny 2
 * Forsaken