What people tend to forget is that they weren't always monsters. Spawned from the panicked despair of a society on the verge of destruction, the Ender Knights had undertaken a responsibility that was more than anyone's burden to bear. And bear it they did, until the bitter end – and beyond.
The world now known as Minecraftia by its sparse, intrepid inhabitants was not always the desolate playground it is today. Who carved into the earth and created those now-silent mineshafts to begin with? Who entombed the spawners of the Nether's unquiet legions within ivy-coated stone? Who inhabited the vast and sprawling strongholds to begin with? The answer is the first generation of men and women: those who came from nowhere and moulded the land as their own. These adventurers united occasionally and formed great city-states, which spread like moss over wet rock into nations and countries. Inevitably, war and conflict erupted where the borders met and many lay dying between the flags of their homelands until diplomacy was reached. A great utopia arose from the ashes of conquest. Peace reigned throughout the land, then known simply as Infinia (as far as the greatest explorers travelled, they could see no limits).
Centuries passed; centuries of technological advancement and the discovery of magic, and the intertwining of these to form wonderous inventions and devices. All seemed well, and perhaps might have remained so until a group of careless young scholars made a fatal error. They brought the purity of flame upon the mystic corruption that obsidian naturally possesses.
The dancing violet sparks that the reaction created aroused their intrigue, and before long the first Portal to the depraved realms of the Nether was constructed. The scholars stood before the shimmering, writhing gateway and boldly passed through, innocently unaware of the horrors their curiosity had wrought for Infinia.
They were slaughtered, as were their worried successors, as were their anxious followers and as were the horror-stricken batch that was sent reluctantly through after that. Fire rained in showers from terrifying beasts of the crimson sky; spiders tore, ripped and desiccated those they caught; strange scarlet towers with empty, sunken eyes and alert expressions emerged from the mist and exploded in a nova of flame and energy where they fell. Not even the greatest warriors could halt the tide of the Nether's unholy beasts, and it was soon discovered that the link of the Portal was not a one-way interaction. The spiders spread through in swarms, followed by the towers which adapted to the new plane and became an unsettling swamp-like green – the floating monstrosities remained, but made short work of those who tried to stem the flow from within.
The governing bodies and councils of the civilised world were distraught and desperate; anything that could be done must be done, for now the unholy magic of the Nether was spilling through and tainting the land. Those who fell dead rose again, with hatred in their tormented screams and hunger in their maws. The ancestors of the nation were stirred from their millennia-long rests and summoned as warriors of evil, taking up arms and striking down their descendants with stuttering, unnatural movements and Godless bloodlust. Even the world of Inifinia seemed intent on the people's destruction, as a gooey pus began to collect upon the surfaces of their deepest caves and inner sanctums and took the form of gargantuan, globular abominations, engulfing petrified refugees by the dozen and corroding them within their grotesque masses. Something had to be done, and only one option remained.
The magi and scientists of the nation worked tirelessly and in tandem until they came to a bitter conclusion: the only way to defeat the hordes of the Nether for good would be to infuse a group of brave souls with its unnatural black magic and send them through the rift, so that they might find the source of the strange power and destroy it. Only then could they be saved from armageddon.
As was planned, so it was done: a group of veteran paladins, weary from years of fruitlessly defending against the Nether's armies, volunteered for the suicide mission, intent on righting the unholiest of wrongs as their swan song. The magic of the Nether was harnessed within small blue jewels that had been found on the far side of the Portal and given to each of the paladins, who were then known by the idolising and grateful public as the Ender Knights – the only ones who could bring an end to the Hell that had claimed Infinia.
They stepped through the Portal without ceremony or delay, brightly-glowing swords at hand and jewels tethered around their necks. The power of the jewels, which the paladins came to know as their Ender Pearls, was unanticipated; the undead were smote in vast swathes by a swing of the sword; spiders were utterly obliterated by a mere slash of the wrist; the towering, explosive creatures fell harmlessly to the ground and did not detonate when the Ender Pearls were the work of their doom. Even the sky-beasts, raining their flames down harmlessly upon the divine Knights could not endure the might of the warriors and fled at their sight – where they were slain and fell, the ground took a glowing quality and became like a crystal. The Knights came to use this as their light as they sought the Nether's mysteries.
Eventually, after days of courageously searching the depths of the realm, they came upon a chamber set deep in the now blood-coloured terrain. Contained therein was a peculiar mirage, a shifting and morphing patch of purple-black energy floating in the centre of the room. Shocks of indigo lightning crackled around its surface. As the Ender Knights stood perplexed and confused before this strange apparition, the room was filled with malicious laughter that shrieked and screeched so that the Knights were doubled over, hands upon ears. When the banshee cackle subsided, there stood a spectral form – that of a woman, whose scarlet hair swirled around her impish features and dissipated into red mist at the ends. Likewise, her legs from the knee down seemed to also change into the strange gas and came away from her in clouds. She identified herself as the Netherwraith, the Queen of the plane, and – recognising their might as warriors – gave them a proposition. The Netherwraith agreed to withdraw from the realm of the living, if the Ender Knights would sacrifice themselves and serve her eternally as instruments of her will. Seeing no other way and knowing they would not live if they disagreed, the Ender Knights accepted the deal with great bitterness and spite.
She took of them their weapons and armour and contorted their bodies: limbs stretched until they were gangly and useless, body blackened and encrusted with perpetual darkness, eyes dimly glowing with the infernal purple of the Nether's energy. She allowed them their Pearls as tokens of their crusade, but expelled all power they had held. Only then were they released back through the Portal.
The Netherwraith's word was as good as any of them could have expected: the legions had withdrawn, but not before reducing the kingdom to rubble. Fallen citizens decayed in the streets, helpless in the absence of their greatest warriors; whole cities smouldered and burnt for weeks on end; once-great castles were little more than heaps of stone and brick. The undead remained, although greatly weakened after the energy from the Portal was removed – so brittle were they that the light of the Sun was enough to melt their bones and cook the flesh from their bodies. The towers had shrunk to the size of men and sown their larval seeds within the earth. Spiders lacked the furious might of the Nether, but still attacked during the night as this was the time they were overtaken by memories of war and conquest.
The Ender Knights wept and lamented, and set to deconstructing the remains of the kingdom they had given up everything for. As years passed they slowly forgot themselves and went mad, twisted and rabid minds locked in the prison of a mutilated body and filled with primal fear and hate when their nightmarish form was gazed upon. But still they cleansed the land of the remains of their civilisation, so that future races might have a chance to succeed where they hadn't. They were driven by motives they didn't understand. It caused them to wander purposelessly, to uproot chunks of land and inspect them cluelessly, to gather the Ender Pearls of their fallen comrades; tokens of a sacred brotherhood long fragmented. An instinctive loyalty to the Knights they were before.
But the noble souls who made the greatest sacrifice for the greatest cause are less than Knights now. They're husks, hollow shadows who roam restlessly with only the tattered shreds of their glory lingering somewhere within a tortured shell. But the people know not of their bold and glorious history, nor their tragic and woeful downfall. They only know what they are, and they call them the Endermen.