Long before the founding of Equestria, when unicorns, pegasi, and earth ponies struggled for survival during the hard snows, the first windigos were born. Ponies died to the harsh winters every year, but one year was different. War had broken out between the pegasus and unicorn tribes. It wasn't the longest, but it was one of the bloodiest. The final battle took place on the coldest day of winter at edge of a large valley. At the bottom of the valley lay one of the most heavily populated Earth Pony settlements, its inhabitants trying to shelter themselves from the cold, completely unaware of the events that would take place less than a mile away.
At the first sounds of combat, the sentinels who watched over the Earth Pony city went to investigate. They found themselves in the middle of a slaughter. Both the unicorns and the pegasi assumed that the other had called the earth ponies as reinforcements, that foul play was involved, and killed the sentinels on the spot. Earth pony soldiers were sent when the sentinels did not return from their investigation and they too were killed.
A pegasus scout was sent to find the source of the reinforcements and she soon discovered the earth pony city. Her superior officer, General Thunderfury, sent a troop of soldiers to investigate the earth ponies. This in turn was noticed by the unicorn commander Lady Lazuli, who sent some of her own soldiers to follow. It wasn't long before the scouts were once again locked in combat, this time in the streets of the once peaceful city. The guards attempted to remove the combatants from earth pony land, but nothing could separate the two bloodthirsty tribes. One guard was caught in the crossfire between a unicorn's magic and a pegasus' crossbow. She died lying at the hooves of her leader, Guard Captain Ironmane. Enraged, Ironmane ordered all of the earth pony guards to join the fray.
Meanwhile, the commotion below drew the attention of the ponies fighting above. Looking down to see her forces outnumbered two to one, Lady Lazuli ordered a full retreat to reinforce her troops below. General Thunderfury refused to allow her hated enemies to escape alive and ordered her army to take chase.
Soon, all three tribes were engaged in vicious combat. Civilians ran to escape the chaos but were struck down by the soldiers who, by now, were barely able to distinguish friend from foe. This further enraged Guard Captain Ironmane, who galloped to engage the other two leaders in battle. By the time the sun sat, unicorns, pegasi, and earth ponies alike lay dead or dying in the bloodstained snow. By morning, there would be no survivors.
Never in the history of ponykind had there been so much raw disharmony in one place. The last thoughts of the ponies who had died quickly were those of hatred towards their enemy. Those who saw their comrades fall fought with vengeance and died in despair, knowing that they were unable to deliver retribution. The earth pony civilians who were slain were filled with terror of the invading tribes and anger that they had flooded the peaceful valley with blood.
Most of the ponies died of the cold that night. They lay wounded beside their enemies as snow began to cover their bodies, too weak even to shiver. Some of them realized in their final moments the horror of what they had done and were overtaken with grief. They exchanged last words with those they had once fought to kill, tears freezing to their faces. The rest died fighting to move their bodies in defiance for just one more second.
General Thunderfury, Lady Lazuli, and Guard Captain Ironmane were the most hateful, each one hating the other more than the rest of their armies combined. Lazuli's horn was lodged in Thunderfury's ribs and she stared unblinkingly into Ironmane's eyes until her eyes froze. The pegasus tried to pull away, but the horn was stuck fast, frozen in place. Her jaw was locked around Ironmane's throat and her broken wings twitched slightly as if aching for the sky. Barely able to breathe, Ironmane stared back into Lazuli's frozen eyes, reaching a shivering hoof forward as if to be the last to strike a blow on her enemy.
The ponies who died in the cold that night never made it to the afterlife. Their souls strained to ascend to the heavens, but their hatred kept them tethered to their bodies in the realm of mortals. The bitter, bone-chilling winds of the howling blizzard that night mingled with the restless souls until they ripped them from their hosts to become one with the wind.
The storms carried them to the highest mountain in the Frozen North where the clouds never parted and the sun never shone, where the world was shrouded in eternal winter. The only traces of life were the frozen husks of the few dead ponies who had dared to venture to its peak.
High above the peak, the souls of the fallen gathered snow and ice until they were frozen specters of their past selves. They howled in eternal torment, feeling only the remorseless, biting cold as they galloped with the winds of the swirling storm.
Every so often, one would swoop down to the dead pony corpses that inhabited their mountain home, hoping for even the slightest bit of warmth. They could roam Equestria as they pleased during the winter seasons. As spring began and the snows receded, the warmth of Celestia's sun forced them to return to their cold, dark mountain.
Every winter, their numbers grew. They brought the blizzards to every door and with them, all of the rage and hatred from their past lives. They would spread across Equestria like a plague, sparing only those with fire in their homes and love in their hearts. Ponies with nothing to burn would rarely survive, very few felt love that was strong enough to overcome the storm . The spirits would circle closely but never descend far enough to kill their victims. Some survivors noticed that they appeared to be in pain when they swooped too close to protected ponies. The spirits would scream and return to their home at a flying gallop without looking back.
They were sometimes referred to as Revenants, Liches, and Winter Wraiths. It was a wizard's apprentice, a young pony known as Star Swirl, who gave the spirits the name that has been used ever since.
He called them 'Windigos.'