One of the fiercest and most cunning characters in the world of The Witcher is Emhyr var Emreis, Emperor of Nilfgaard. Born to Emperor Fergus var Emreis, Emhyr was 13 years old when his father was deposed, imprisoned and tortured in a coup led by someone known as the Usurper. The Usurper's sorcerer, Braathens, then put a spell on young Emhyr that turned him into a hedgeho., The Usurper hoped to prompt Fergus to grant legitimacy to the coup, but Fergus was killed and Emhyr set free in the woods with the royal hounds after him.
While in the woods, Emhyr discovered that Braathens hadn't even done the spell properly, for every night at midnight he returned to his human form until dawn. He managed to survive and escape the woods, but not before meeting an astrologer that led him toward the north to find a cure for his affliction.
Traveling through the Northern Kingdoms, Emhyr used the name Duny, Urcheon of Erlenwald. He was in Cintra in 1237 when he happened upon Cintra's King Roegner wounded and saved him. The King offered him a reward, and he invoked The Law of Surprise as his boon. Unbeknownst to King Roegner, his wife, Calanthe, was pregnant with their daughter, Pavetta. The Law of Surprise deemed that she belonged to Duny, but he did not return until Pavetta's fifteenth birthday.
Emhyr visited Pavetta in secret for sometime before Queen Calanthe arranged for her to be presented to a series of political suitors looking to ally themselves with Cintra. While Geralt of Rivia was in attendance, Duny arrived to claim his Child Surprise, but Calanthe denied him after tricking him into removing his helmet before midnight and revealing his true face. She tried to convince the witcher to kill him, but Geralt refused, instead going to Duny's aid with Mousesack when Calanthe's men and the other suitors attacked him. However, Pavetta's Source power erupted, sending furniture and people flying in all directions.
Because Geralt saved him and helped to break his curse, Duny granted him a boon; Geralt claimed the Law of Surprise. Pavetta was already pregnant, and the child she and Duny had became Geralt's child surprise, Cirilla of Cintra.
When the sorcerer Vilgefortz presented Duny with a prophecy and a plan to gain personal renown only the Emperor of Nilfgaard could provide, the two of them plotted his return to Nilfgaard with his family. Calanthe wouldn't have allowed him to take her daughter and granddaughter, so he devised a plan to fake all of their deaths at sea. Pavetta, learning of Duny's plan, smuggled Ciri off the ship before it departed. When Duny confronted her, a scuffle sent Pavetta tumbling into the sea. He and Vilgefortz escaped, with Cirilla remaining in Cintra with her grandmother, believing both of her parents were killed at sea.
Upon returning to Nilfgaard, he resumed his identity as Emhyr var Emreis and led a successful coup against the Usurper to reclaim his throne. He disinterred the bodies of all his political enemies and used their tombstones to pave his ballroom. This brutal and cunning act earned him the elven nickname Deithen Addan yn Carn aep Morvudd, or The White Flame Dancing on the Barrows of His Enemies.
After reestablishing his empire, Emhyr set his sights on the Northern Kingdoms, intent on expanding with the launch of the first Nilfgaardian-Nordling War. After the war, he stirred unrest and rebellion in Cintra before sending in soldiers to quell it and locate his daughter. Queen Calanthe was killed, but Ciri went on the run until she was reunited with Geralt of Rivia to begin her training as a witcher.
Emhyr plotted to marry Cirilla to fulfill a prophecy shared with him by Vilgefortz years earlier. Upon tracking her down, he plotted to kill Geralt and Yennefer before taking Ciri with him. However, after thinking about his plan, he realized how monstrous it was and relented, setting Ciri free and leaving Geralt and Yennefer alive.
In CD Projekt Red's game adaptation of The Witcher, Emhyr did not surface until Assassins of Kings. It was revealed that he was the patron who hired the witcher Letho to kill Kings Demavand and Foltest to weaken the North in preparation for another invasion. He launched that invasion in 1272, taking advantage of the chaos in the North to quickly conquer Temeria, Lyria, Rivia and Aedirn.
Emhyr reached out to Geralt to locate Cirilla, whom he wished to make his successor to the throne. He made his first physical appearance in Wild Hunt, when he brought Geralt and Yennefer into Nilfgaard to reunite them and ask them to help him find Ciri.
Emhyr's fate is entirely dependant upon the player's choices. If Radovid and Dijkstra are both killed, he is successful in overtaking the North and exterminating all who oppose his rule. If Dijkstra or Radovid survive, Emhyr var Emreis is assassinated by internal spies after losing the war. If he wins the war and Cirilla survives her own adversities then visits him, he abdicates the throne to her.
Given everything Emhyr suffered at the hands of the Usurper and his sorcerer, it was no wonder he went a little mad -- and not just with power. His plans to secure his rule in the north by marrying his own daughter went well beyond the power hungry plot to overpower all within his grasp. He was made powerless and vulnerable, tormented and stripped of all that mattered in his world, and for that he made certain that anyone who stood in his way would not only suffer, but fall for their crimes against him.