The W'rkncacnter were mythical chaotic entities (or was just one entity) that were as ancient as the universe and of were unimaginable power. They may only exist in certain timelines.
Its existence is hinted at in the storyline of Marathon 2: Durandal, and its release from Lh'owon's star becomes a major plot point during Marathon Infinity.
S'pht mythology
The W'rkncacnter is a central part of the S'pht's founding mythology. According to terminals found in the bunkers under the Citadel, the spread of the W'rknacacnter caused Lh'owon's founders, Yrro and Pthia, to colonize the planet. After the W'rkncacnter's arrival, Yrro trapped the creature in Lh'owon's sun and gave Lh'owon to the S'pht.[1]
In primordial space, timeless creatures made waves. These waves created us and the others. Waves were the battles, and the battles were waves. Fleeing all W'rkncacnter, Yrro and Pthia settled upon Lh'owon. They brought the S'pht, servants who began to shape the deserts of Lh'owon into marsh and sea, rivers and forests. They made sisters for Lh'owon to protect and maintain the paradise. When the W'rkncacnter came, Pthia was killed, and Yrro in anger, flung the W'rkncacnter into the sun. The sun burned them, but they swam on its surface. – Six Thousand Feet Under, Terminal 4
Marathon Infinity
Marathon Infinity describes the W'rkncacnter as a race of beings who "live in chaos, creating it around them." Over time, they have become imprisoned in the more "chaotic" aspects of the universe: stars, storms and black holes are all named as prisons. Freeing a W'rkncacnter is possible, but very difficult (given the nature of their prisons). One would have to be insane to even try: their ability to generate chaos enables them to destroy on a cosmic scale. The W'rkncacnter are present in the myths of thousands of worlds, most of which are now uninhabitable, and tales of their destructive power have survived all over the galaxy for over 60 million years.[2]
When the Pfhor uses the trih xeem device to send the star into an early nova, the creature is released to the horror and destruction of both the Pfhor under Tfear,[3][4] and Durandal.[5]
Uncertainties
Whether W'rkncacnter is a singular entity or an alien race is unclear. It is possible that the W'rkncacnter are a race that is represented as a singular entity in the S'pht mythos, much like their mythological character Yrro has been speculated to be a singularization of the Jjaro. Durandal/Thoth in Marathon Infinity describes the legendary W'rkncacnter as having distinct identities. Another theory is that the W'rkncacnter is both a multiple and singular entity, in some incomprehensible way (possibly multiple manifestations of a single entity). Due to the contradictory descriptions, it is entirely plausible that the W'rkncacnter is a hive mind or functions in a fractal way, possessing multiple bodies/incarnations that can either act separately or as a single entity and would be identical on any given scale. Given the being's chaotic nature, almost anything is possible.