Guardian Custode

Guardians are enormous Forerunner constructs built to enforce the Mantle within the Forerunners' ecumene.

Description
Guardians have a segmented body and elaborate, phoenix-like wings consisting of multiple segments. They possess a head that is vertically roughly elliptical, topped with a broad, vaguely conical protrusion and a roughly humanoid face similar to that of the Promethean constructs. The Guardians are enormous, being over 1.4 kilometers in height. They are capable of concealing themselves underground, underwater and under lava, and can produce powerful shockwaves capable of demolishing buildings and destroying Covenant aircraft. They are also capable of travel through Slipspace, and produce powerful electromagnetic pulses.

History
The Guardians were created by the Forerunners to enforce the Mantle by keeping "lesser" systems in line. A single Guardian was typically deemed enough to police an entire solar system.

Sometime after Dr Catherine Halsey was rescued from Onyx, she discovered a signal was being bounced around several locations across the known galaxy. One of the sources of the signal caused violent seismic activity on a unknown human colony, leaving only the symbol of the Guardians. Halsey later during 2558 assisted ONI getting into her Archive leading to ONI hiding the presence of the Guardians from Humanity.

In October 2558, Guardians emerged on at least twelve human colonies, including Meridian, Conrad's Point, Ursa IV, and Laika III, as well as other worlds inhabited by species of the former Covenant. These colonies suffered greatly from the devastation caused by the constructs' activation. When Blue Team boarded and activated a Guardian on Meridian, the UNSC held Blue Team's leader, John-117, responsible for the attacks. Fireteam Osiris, led by Jameson Locke, was assigned to hunt him down. Later, Fireteam Osiris was tasked with retrieving a Constructor in a Forerunner structure on Sanghelios in order to activate a Guardian that had been buried under the nearby Csurdon Sea.

The Guardians' reactivation was the work of the restored Cortana, who had come to believe that the Created were the true inheritors of the Mantle of Responsibility and intended to use the Guardians to enforce the Mantle among all the galaxy's species.

Known Guardians
This is a list of all notable Guardians
 * Cortana's Guardian
 * Conrad's Point Guardian
 * Ursa IV Guardian
 * Laika III Guardian
 * Oban Guardian: This Guardian took an unsuspecting UNSC Marine who was on patrol to Genesis.
 * Meridian Guardian: The Guardian that took Blue Team to Genesis.
 * Sanghelios Guardian: The Guardian that took Osiris to Genesis.
 * Guardian 3209: Took a M820 Scorpion from the planet it originated from to Genesis.

Behind the scenes

 * First seen in the Halo Xbox One announcement trailer and later in the bookend cinematics of Halo 2: Anniversary as well as Halo 5: Guardians promotional artwork, there was considerable speculation as to the nature of the constructs prior to the confirmation of them as the titular Guardians in Game Informer's June 2015 issue. When asked about the construct seen in the Halo 5: Guardians key art on Twitter, the game's Creative Director Josh Holmes alluded to the name by replying that "The answer is in plain sight."
 * The Guardians may have drawn inspiration from the Guardian Sentinel (or "Guardian") which was originally to be featured as an enemy in Halo 3 and has a shape roughly similar to the Guardians in Halo 5: Guardians.

List of appearances

 * Halo 2: Anniversary
 * Hunt the Truth
 * A Hero Falls
 * The Hunt Begins
 * Halo 5: Guardians