A fierce and unrelenting enemy, the Wild Hunt of The Witcher franchise was believed for centuries to be a group of wraiths galloping across the sky on their undead steeds. People superstitiously surmised they were an omen of war, heralding oncoming doom across the Continent. In Skellige, they are known as the Wraiths of Mörhogg, but this menacing pack of Aen Elle were actually elves of Tir Na Lia, and they called themselves Dearg Ruadhri -- the Red Riders.
Ereden Bréacc Glas began as their general and eventually became their king. Then, he led them across the realms in search of slaves to bring back to the capital of their world, Tir Na Lia, to serve the Alder Folk. However, the Wild Hunt did not originally come from Tir Na Lia.
When the Conjunction of the Spheres created chaos in the cosmos, a group of Aen Siedhe elves broke from their kin and the main world to to cross through the portals and find a new world. There, they began to refer to themselves as the Aen Elle -- the Alder Folk.
Not long after their arrival, they discovered the world was not uninhabited. Humans and unicorns had already been living there, so the Aen Elle waged war on the humans and destroyed the population. For a time, they thrived in this new world. They built beautiful structures, including a grand palace called Tir Na Lia, and the city in which it was built became their capital.
It seemed they wanted for nothing, but they began to crave servants to see to their needs. The unicorns, which they were constantly at war with, were unsuitable for the task, so the Wild Hunt forced the sentient creatures to open the Gate of the Worlds so they could cross through and find slaves to bring back to Tir Na Lia. King Auberon Muircetach created a cavalry and appointed the warrior Ereden Bréacc Glas to lead them into alien worlds in search of beings to enslave. The cavalry wore red cloaks, earning them the name the Red Riders.
Eventually, the unicorns took access to the Gate of the World away, severely limiting the Wild Hunt's travel. They found a way around this issue using powerful mages, known as navigators, to open portals. Only a small numbers of riders could pass through, which severely limited their slave haul. The Wild Hunt also began traveling through spectral projections of themselves, which eventually led people to believe them to be wraiths.
They traveled to many worlds, projecting themselves in the skies as specters sailing in a ghastly ship known as Naglfar, but there was one world they preferred traveling to the most: Their home planet. Over the centuries, this planet had become overrun by humans, and humans made the perfect slaves. When the Hunt appeared, usually in winter, they would raid the lands for months, abducting choice specimens to carry back to their new world.
In Andrzej Sapkowski's literary explorations of the world of The Witcher, the Wild Hunt became obsessed with Cirilla of Cintra, due to the old blood in her veins. They pursued her relentlessly, eventually bringing her back to Tir Na Lia, where they wanted her to produce an heir for Auberon. As a direct descendant of his daughter, Lara Dorren, the magic in Ciri's blood would pass on to her heirs.
The Aen Elle craved this magic because it would enable the Wild Hunt to access the World Gate. Ciri resisted at first, but she eventually relented. However, before she could give Auberon an heir, Eredin poisoned the king with an overdose of a powerful aphrodisiac and took the throne for himself.
The Hunt continued to pursue Ciri by tracking the use of her power. When Yennefer and Geralt were killed, she used her magic to bring them back and transport them to Avalon, where they could rest. She became a pupil of Avallac'h, and as he taught her how to use and control her power, the Hunt was always one step behind her.
Eventually, they realized the easiest way to get to Ciri would be to capture the people she loved. They invaded Avalon, took Yennefer and carried her off. Geralt went after them, returning to the Aen Siedhe world and chasing the Hunt until he caught up at a Hanged Man's tree. There, Geralt bargained with Eredin, offering himself in Yennefer's place. Eredin accepted, and for a time Geralt rode with the hunt, which had the desired effect Eredin hoped for: Ciri came out of hiding and rescued Geralt, who had developed amnesia, and placed him near Kaer Morhen, where Triss and the witchers later found him at the start of CD Projekt Red's first Witcher game.
Ciri went back into hiding and continued training with Avallac'h. Eventually her desire to return home prompted them to cross through the portals. The use of her power alerted the Wild Hunt, who confronted her in Ard Skellig. She managed to escape again, but was badly injured. It wasn't long before they caught up, attacking the village that granted her refuge and killing nearly everyone.
The Witcher 3: Wild Hunt explored Eredin's plot to capture Ciri, urging Geralt and Yennefer to combine forces to protect their adopted daughter. In a brutal battle to save Ciri, Geralt dealt a killing blow to Eredin. With their king destroyed, the Hunt was disoriented enough that the Skelligen forces obliterated the rest.