— Marionette Control Panel
Mordremoth's existence did not become apparent to most Tyrians until early 1327 AE, when it awoke. It was, however, mentioned in ancient dwarven texts and jotun stalea, although no details other than its existence were ever made clear. Additionally, the Inquest had been conducting experiments structured around the existence of six Elder Dragons for a while, indicating they had some prior knowledge of its existence.
 Pre-awakening evidence
The Infinite Coil Reactor, where the Inquest are attempting to harness Elder Dragon energies (among other things), is built in a hexagonal structure with six corners, each containing a "zone": Black, Red, Violet, White, Blue, and Green. Four of the zones (Black, Red, Violet, and White) are known to correspond to Elder Dragons (Zhaitan, Primordus, Kralkatorrik, and Jormag respectively), containing dragon minions, and the under-construction Zone Blue, although empty, contains a pool and occasional idle dialogue implies that it is intended to house a captured minion of the deep sea dragon. Zone Green has a nature theme, including poisonous Death Blossoms, but is otherwise empty.
The Crucible of Eternity is the interior of the Infinite Coil Reactor, and is where the experiments on Elder Dragon minions are performed. Three labs are able to be visited - Experimental Lab Red, Experimental Lab White, and Experimental Lab Green. Again, Lab Red is related to Primordus, and Lab White related to Jormag. Lab Green contains a multitude of plant creatures, including Nightmare Husks and Nightmare Hounds. Each zone also houses a powerful minion, respectively the Evolved Destroyer, Bjarl the Rampager, and the Evolved Husk, implying a connection between the jungle dragon and the Summoned Husks utilized by the Nightmare Court. Also Subject Alpha uses various skills that are related to the Elder Dragons: he summons Bone Tendrils (Zhaitan), imprisons players in crystal (Kralkatorrik), and has three attacks named Teeth of Primordus, Teeth of Jormag and Teeth of Mordremoth, hinting the Dragon's name long before the confirmation.
There are other, potential, possibilities of Mordremoth's pre-awakened influence, but none are confirmed. The strongest two are: Gamarien, whose Wyld Hunt calls him to protect Wychmire Swamp and fears that a "much darker force" than the Nightmare Court is the cause behind the large number of Summoned Husks present there. And then the Veteran Rotting Oakheart in Thaumanova Reactor, which had dealt with dragon energy experiments like Crucible of Eternity, and in turn the Champion Ancient Rotting Oakheart which functions and looks the same, and is mentioned to be "corrupted" (though unknown if dragon corruption or another more mundane idea).
The sylvari Scarlet Briar worked to awaken Mordremoth for over a year, driven by insanity and her encounter with an entity while in Omadd's Isolation Module. Mordremoth finally woke when Scarlet Brair's drill, The Breachmaker, struck the ley lines beneath Lion's Arch. This resulted in a magical chain reaction, culminating with the awakening of an Elder Dragon somewhere west of Thaumanova Reactor, across an arid plain in a vegetated area presumed by players to be Magus Falls.
Unused 2007 concept art by Kekai Kotaki.