Tyat'Naghra

Tyat'Naghra, the Time Serpent, is an Old Being spawn in the form of a massive snake that is capable of moving through time.

Birth
Tyat'Naghra was concieved when Ygakdne mated with Nagrkenteki the Voracious. It's ability to travel through time as well as space allowed it to avoid Fon'Tdak when the Wolf came hunting after Nagrkenteki's brood. Tyat'Naghra traversed the cosmos even after the fallout of Zykezx's Conquest, and was reverted to the form of a cold, grey fire. Shortly before the Conquest, when Fon'Tdak realized he would be unable to track the Time Serpent, a prophecy was foretold that if the last of the Ancient princes were to be devoured by Tyat'Naghra then the Ancients' legacy would end.

Fulfilling the Prophecy
Displaced out of time via the Chasm of Time and Tom's sacrifice, Tyat'Naghra arrived as the grey conflagration upon the desolate moon-world. He traveled from there to a nearby star, upon which he spread until the entire star collapsed into a cold, dense mass, from which he hatched in his true serpentine glory.

With the Apocalypse Lords doing battle with Lossoriawath, the last of the Ancient Princes was already on the run. The arrival of Tyat'Naghra might have marked the fulfillment of the prophecy, but for Lossoriawath's possession of the Temporal Matrix, which allowed him to also move through time. With the Guardian defying prophecy in order to fulfill it, the other three Apocalypse Lords were able to pursue Lossoriawath and separate him from the Matrix. In his desperation, Lossoriawath forgot to keep track of the space where Tyat'Naghra phased out of time, and was caught unawares as he ran up the stairs. He was devoured, marking the end of the Ancients' legacy: humanity.

John Beckett remarks that they had pursued Lossoriawath so far into the future that the end of human civilization at this point was not a failure. They had a good long run. Tyat'Naghra intended to vanish after consuming Lossoriawath, travelling off to sate his appetite upon the last prospects of this waning civilization at the end of the era of man. However, the Apocalypse Lords used their combined power to seal the Time Serpent within the S'cha'ckl-ueu Arc, staving off the Triangle Holocaust's world-ending consequences until the Ravager's opening of the Arc and the creation of the Disrupted Timeline.