Duke Felix Aaron Thenardier is one of the main antagonists of the fantasy light novel and later anime series Lord Marksman and Vanadis, or Madan no Ou to Vanadis in the original Japanese. Felix a high-ranking ruler in the fantasy country of Brune (an obvious paralell to medieval France, as all locations in the world of Vanadis are analogs to various parts of medieval Europe), and a relative of the king. After the king was driven mad by grief over the death of prince Regnas, Thenardier fought a civil war with his main rival, Duke Maximilian Bennusa Ganelon.
At the same time, a Brunish army was defeated by the armies of a rival kingdom of Zchted at the battle of Dinant. One of the few survivors, Tigrevrmud Vorn, Earl of Alsace, was personally taken prisoner by Zchtedi Vanadis or "war maiden" Eleonora Viltaria, who was also the ruler of the territory of Leitmeritz.
Thenardier considered Tigrevrmud's capture as shameful, and view Alsace as a vulnerable territory to invasion by Zchted or Ganelon, so he ordered an army under his son, Zaien Thenardier to destroy the territory to deny it to the enemy, as well as to kill or sell into slavery the residents as punishment both for Tigrevrmud's failure and a large debt the province owed him.
Meanwhile, Tigrevrmud befriends the Vanadis Eleonora in spite of being his captive, impressing her greatly with his archery skill. The Vanadis agrees to aid her new friend in defending his home on the condition that it be placed under Zchtedi administration.
Eleonora and Tigrevrmud defeat Zaien's army first in Tigre's hometown, and then at the Battle of Molsheim, where Tigre personally kills Zaien in spite of his dragon mount by combining the power of Elen's magic longsword and Tigre's family heirloom the equally powerful magic "Black Bow".
Zaien is infuriated by the death of his son, and has his ally, Ludmila Lourie, a rival Vanadis of Elen's attack her territory, as well as attacking Alsave himself. Ludmila, however, defects to Elen's side after a short battle. The combined force of Elen, Ludmila, and Tigre become known as the Silver Meteor Army, after their banner.
The loss of his ally, Thenardier continues his fight, temporarily allying with his rival, Ganelon in order to defeat Tigrevrmud and Eleonora. Thenardier and Ganelon send their most skilled troops, the Navarre knights, led by Sir Roland to attack the Silver Meteor Army. This inflicts the only defeat on the army in the Brunish campaign, at the Orange Plains. Roland, however, is later defeated in a second battle.
At this point, Ganelon has Roland executed for his failure, an act that infuriates Thenardier. However, he is force to delay his fight against Ganelon in order to fight an invasion by the southern kingdom of Muozinel. Thenardier's forces play an important role in defeating a Muozinel naval invasion, but the main Muozinel land forces are defeated by Tigrevrmud Vorn and Ludmila Lourie's forces. For their halting of the invasion, the Silver Meteor Army are hailed as heroes.
After the invasion, Thenardier continues his quest for vengeance against Tigrevrmud and Eleonora with an army of 24,000 men and five dragons. This force meets Tigre and Elen's forces at the Battle of Vincennes, where Elen and Tigre's magic weapons managed to slay the dragons, and their mastery of military strategy wins them the battle.
Even after the loss of his dragons, Thenardier keeps fighting Tigre and Elen, sending a squad of 20 of his best men to ambush them in the holy grotto of St. Groel. During the incident, Thenardier proves himself such a skilled swordsman that he is able to match even the superhuman Vanadis in a swordfight, armed with his massive greatsword.
Thenardier's final battle takes place at Mereville, where he engages him in personal combat, intending to charge him on his horse and kill him in close combat. However, for some reason, Thenardier wears heavy plate armor, but no helm. Thenardier deflects Tigre's first few shots with his shield, but the final arrow in his quiver struck Thenardier in the forehead, killing him almost instantly- Thenardier only managed to get out the words "Brune is..." before he died.
Zaien is something of an anti-villain as, while he is a power-hungry Social Darwinist, viewing the weak as not worthy of his concern- as noted when he attempts to destroy Tigre and his poorer province of Alsace, he is still a man of honor, who was outraged at Ganelon's execution of Roland. Thenardier also loved his family, and was infuriated by the death of his son.