For years we had speculated the nature of the universe, as a part of which our lives unfolded, and questioned the possibility of our own solitude on this verdant geoid. But whilst we looked up to the skies, searching the infinite darkness, our answer came to us from a place we could not have known true, nor could we have searched. There exist side by side, an infinite number of universes that comprise what we now call the Multiverse; an endless void of parallel possibilities. We took pride in our feats of advancement as a space-faring civilisation until a void-faring one came to our doorsteps.

We did not speak their tongue, nor could we learn it, but they learned all of ours in a short time. They had come seeking refuge from their dying world and had found just a single planet conducive for their habitation and survival across the Multiverse.

They called themselves the Xitrakk but we called them Voidwalkers, and that name has persisted to this day and will continue to do so, it seems.

The Voidwalkers were a species of shapeshifting alien creatures, averse to being called extraterrestrial for they had inhabited a terrestrial planet, just like ours. Scholars have referred to them as homo-superiors; an evolved, improvement on what we are.

They were born with the abilities to move through space and time by means of teleportation, psychically harness the basic elements of plasma, wind and ice - which we learned was common on their home world - and could morph their bodies with no difficulty whatsoever, albeit often choosing to remain anthropomorphic.

We welcomed them with open arms; the hospitable embrace of a naive species. They lived among us - first as strangers; feared and marginalized, then as equals; adored and idolized for their heroics, scientific knowledge and superhuman displays.

They were celebrities, athletes, superstars but what we did not know, was that they were a also a disease.

We discovered the source of this pandemic in time and learned that the Voidwalkers had known that their presence on our world would lead us to this; the result of exposure to their biological effluvium.

They had not intended to eradicate mankind, but would watch it happen if it meant their species would be ensconced contently on our planet.

It became clear to us, the genocidal effects of this cohabitation. It was us against them - on our world, our planet. At first, we could not fight them. They were superior and had withheld enough knowledge from us to best us in military and technological warfare. We were cro-magnon men up against Sentinels. They had however, underestimated the adaptive nature of the human immune system and when we, cowering and hoping on our side, began to experience second generation mutations that put us on par with these malevolent visitors, it was a surprise; pleasant to us and fatal to them. The divine intervention of our maker, perhaps.

Humanity's first heroes banded together, displaying courage and bravery in a time of chaos, panic and anarchy, they thrust themselves into battle against an enemy they could not match in anything but brute force with powers they had yet to fully understand. It was a hail Mary with our backs against the wall.

The "war" lasted long enough for our faster breeding species to outnumber the enemy with mutant hordes raised to do battle and nothing else.

Our numbers were growing and theirs dwindling; it was still a genocide, but now, the shoe was on the other foot. In a last gasp effort, the Voidwalkers retreated, utilising an ability they had not shared with us; one that took everything from them and cost more than it was worth. They had no choice.

The Sentinels are a variety of government-owned mutant-hunting robots. Sentinels are designed to detect, hunt, apprehend and incapacitate mutants. While many are capable of tactical thought, only a few are self-aware.

Sentinels are technologically advanced, and have exhibited a wide variety of abilities. They are armed (primarily with energy weapons and restraining devices), capable of flight, and can detect mutants at long range.

They possess vast physical strength, and their bodies are highly resistant to damage. Some are able to alter their physical forms or re-assemble and reactivate themselves after they have been destroyed.

Sentinels Patrol cities (particularly areas that have a high mutant population) occasionally but are mostly dormant at various stations until deployed or a scheduled patrol date. They are capable of detecting individuals with the X-gene, thanks to Cerebro and are responsible for informing the League of the births of new mutants in their vicinity.

They are deployed as a countermeasure to rogue mutants and a solution to thwart potential problems but most times, they only serve to escalate the situations they are involved in and rarely any conflict in which they take part ends without damage to mutant individuals and property.

Sentinels are not programmed to take action against non-mutants and will not lift a finger to harm them unless as collateral damage in the pursuit or apprehension of a mutant.

Types

There are 3 distinct types of Sentinels that currently exist, each with its own advantages and disadvantages:

Mark 1

The most commonly seen and deployed Sentinels, ironically the most expensive to manufacture and maintain as well, Mark 1s stand 20 to 30 feet tall and possess the following abilities:

-A vast array of powerful energy weaponry
-Tactical missiles
-Various items for detaining people, tendrils and energy nets, freeze rays
-The ability to fly using thrusters

Mark 1 Sentinels are powerful engines of destruction (weaponry aside) and are incredibly durable, and resistant to Extreme temperatures.

They are made of high-quality alloys and cybernetic composites. They also have various devices e.g. DNA and Infra Red scanners and sonic probes capable of detecting & tracking mutants.

Mark 1s are not sentient but are expertly programmed and very lethal.

They excel at apprehending groups and taking on large numbers of enemies. Mark 1s are quite simply the Government's wrecking balls.

Mark 2

The Nephilim are smaller, manned Sentinels that possess all the abilities of a Mark 1 coupled with the intelligent maneuvering of a human pilot, speed and aerodynamic advantages that come with their size and design and a dense, non-magnetic composition.

They stand 15 feet tall with a pilot chambered at the core, and though their blasts pale in comparison to that of the bigger machines, they are far more durable and incredibly difficult to beat.

Nephilim are only deployed in special circumstances where their unique differences will guarantee an advantage when combatting mutant elements.

Mark 3

Only one Mark 3 exists. Its composition is unknown and it is said to be capable of adapting to all known mutations with a continuously increasing database. The Mark 3 was designed by Cerebro and is in the possession of the UNO.