Anecdotal evidence suggests that the individual bearing the title from at least 1789 was the unacknowledged, illegitimate son of a minor nobleman. He rose to power in the Cour des Miracles in the late 1770s and quickly acquired a reputation for cruelty towards the beggars who paid him tribute, often having limbs amputated from those who failed to make enough money as a means of motivating others. For these acts of cruelty, he quickly became a target of the French Brotherhood.
The Roi des Thunes would later recruit the former tax assessor Aloys la Touche as his enforcer, recognizing his cruelty and economic acumen. Around 1789, the Roi des Thunes became aware of the existence of the Templar Order, and appealed for membership, claiming the advantages of his underground connections.
However, the Grand Master, François de la Serre, refused him membership in the Order because de la Serre did not believe his position was fruitful, stating he had no need for the "intrigues of rats".
The Roi des Thunes vowed revenge on de la Serre, and was later presented with an opportunity to carry it out by the Templar Charles Gabriel Sivert, who was secretly participating in a coup d'etat within the Order, led by François-Thomas Germain.
Germain later accepted the Roi des Thunes and la Touche into the Order. At a party attended by de la Serre in May 1789, Sivert and the Roi des Thunes planned to assassinate the Grand Master. Sivert lured de la Serre out to the palace gardens, where he attacked him.
However, de la Serre managed to fight Sivert off, wounding the latter's face. Nonetheless, the Roi des Thunes snuck up from behind and struck de la Serre with a poisoned pin crafted by Germain, killing de la Serre in moments.
As the two Templars made their escape, Sivert called out the guards and framed Arno Dorian, who had witnessed the murder of his adoptive father. Around 1791, the Assassin Council sent no less than three apprentices to locate and kill the Roi des Thunes, one of whom was Brasseur, an apprentice of Guillaume Beylier. All three failed in their tasks, with Brasseur being personally murdered by the Templar. Upon learning of the Roi des Thunes' involvement in de la Serre's killing, the Council charged the newly-inducted Arno with finding and killing the Templar.
Arno eventually found the Roi des Thunes with the help of the Marquis de Sade, who hoped to take over the Roi des Thunes' criminal empire. La Touche warned his master of Arno's imminent arrival, much to the Roi des Thunes' shock that he had been tracked down so soon.
When Arno attacked the Roi des Thunes who was sitting on his throne, he realized that it was an ambush. The third Assassin killed by the Roi des Thunes was used as a decoy, while the Roi des Thunes and his snipers tried to shoot Arno. Despite this, Arno managed to elude the snipers and assassinate the Templar; using his Eagle Vision to delve into the Roi des Thunes' memories, Arno learned that he and Sivert were not alone in murdering François. After the Roi des Thunes' death, the Marquis de Sade quickly took over his position. Arno also claimed a trophy from the late monarch in the form of the Officer's Pistol, the flintlock which had previously belonged to the Assassin he had murdered.