Fildgor Orcthane, once known as Fildgor Strong-Prince, is a Nord prince born to Queen Mabjaarn Flame-Hair of Skyrim. He is Jorunn the Skald-King's exiled brother and leader of the famed Stormfist Brigade of western Skyrim.
The Vestige encounters Fildgor with his Stormfist and Orsimer allies throughout Eastmarch as they try to usurp the throne from the current High King. He takes on the name Fildgor Orcthane and tries to disrupt the festivities of the Konunleikar in Windhelm, and is considered the region's primary antagonist.
Fildgor was the second son of Queen Mabjaarn, twins with Jorunn and younger brother of then Nurnhilde. While his brother studied the art of the skald at a young age, Fildgor who favored martial prowess explored the western lands of Skyrim to see its people where he met and befriended the Stormfist Clan. Although not of their own clan, eventually he became its leader and formed the Stormfist Brigade, where he and the Stormfists grew in reputation as brave adventurers.
It was during Dir-Kamal's invasion of Skyrim that the Stormfist Brigade was put to the test. Fildgor and the Stormfists took back the beleaguered city from the Akaviri invaders, but not before the Queen and his older sister was killed. With the throne left vacant, Fildgor claimed the throne of Skyrim, only to be challenged by Jorunn who believed Fildgor's warlike intentions would bring ruin to Skyrim. To prevent a civil war, Jorunn challenged his brother to single combat, defeating Fildgor and exiling his brother from his lands. Since then, he has taken on the name Fildgor Orcthane, gathering the strength of his Stormfist allies and befriending Covenant and Orcish forces, waiting for a perfect time to strike against his brother.
Fildgor first makes his presence to the Vestige and his brother Jorunn during the Konunleikar celebrations in Windhelm. Sending a champion to represent the Stormfist Clan in the celebrations, the Stormfist Clan struck during the final contest at the Hall of Trials and charged at King Jorunn and his retinue.
Fildgor then sent his troops to capture Fort Morvunskar. The Vestige arrives with reinforcements from Windhelm, only to find out that Fildgor was only after the remains of Nurnhilde. Fildgor is seen for the first time by the Vestige as he flees the fort, leaving behind his lieutenant Shukul gro-Agluk to deal with the Vestige.
At Fort Amol, Fildgor sent his newly recruited Breton assassin and alchemist Dhalen to disrupt the King's council with the rest of the Pact members. Dhalen and his Covenant assassins assumed the faces of the royal guards through the use of an Argonian substance and infiltrated Jarl Ivannar's manor. Planning to take on Jorunn's appearance, Dhalen was stopped by the Vestige and the Dunmer assassin Naryu Virian, but not before poisoning the king with Daedric poison.
Jorunn manages to live with the help of the Dreamwalker and the Ternion Monks, while Fildgor retreats to Skuldafn. He plans to merge with Nurnhilde's spirit in Sovngarde, forcing the Crown of Freydis to recognize him. This would allow him to usurp Jorunn and become High King. However, Fildgor is stopped by the Vestige. Depending on the Vestige's choice, he can either be killed by the Vestige, killed by Jorunn, or spared and sent to prison.