Lydia: "Why do you care? Why are you suddenly on our side?"
Gerard: "Because it's my name, as well. Marie-Jeanne never left Henri after the death of her brother... And their relationship became more than a partnership. They married, and she took his name."
Lydia: "Argent."
Chris: "Marie-Jeanne was the first Hunter."
Lydia Martin, Gerard Argent, and Chris Argent about Henri and Marie-Jeanne's relationship in Maid of Gévaudan

The relationship between Hunters Henri Argent and Marie-Jeanne Valet.

Throughout Teen Wolf

Season 5

In the flashbacks to 18th century France in Maid of Gévaudan, Marie-Jeanne Valet, known throughout the village of Gévaudan as the most talented hunter of mundane animals, met Henri Argent, a scholar in the study of the supernatural, after numerous citizens were brutally torn apart and murdered by what was believed to be an animal who would eventually become known as La Bête du Gévaudan, or the Beast of Gevaudan.

Henri came into the French Tavern with the body of Emil, the son of the barman, Rene, just as the others in the tavern were both welcoming the return of their fellow citizens Sebastien Valet, Marie-Jeanne's brother, and his comrade Marcel, from the Seven Years War and begging Marie-Jeanne to head the hunt for the Beast. Marie-Jeanne, devastated by the sight of Henri carrying the young boy's body, ultimately decided to lead the hunt, despite her insistence that the Beast was merely an animal rather than something supernatural.

The following evening, the team of hunters had barely had a chance to spread out through the forest in hopes of finally tracking down the Beast before the creature attacked, mauling nearly all of them to death and injuring Marie-Jeanne's leg before suddenly, Henri appeared and used a jar of Mountain Ash to create a barrier around the two of them before the Beast could kill her. Once the Beast got frustrated and left, Marie-Jeanne, dumbfounded by the sight of the shadowy, eight-foot-tall Beast, exclaimed that the Beast was no wolf, leading Henri to call her a fool before informing her that it was a Werewolf.

Marie-Jeanne, who injured her right thigh in the fight, was brought back to Henri's Cabin, which was surrounded by rowan trees (from which Mountain Ash is made) and full of various herbs, plants, and substances from his studies. When Marie-Jeanne began poking around at the materials and asked what the Mistletoe and Wolfsbane was for, Henri initially advised her to put them down before reconsidering and instead revealing that he had spent half of his life compiling the implements needed to survive a Werewolf attack. He went on to offer to teach her what he had learned, which Marie-Jeanne accepted, though she made it clear she had no intention of learning how to survive a Werewolf-- she wanted to learn how to kill one.

Combining Henri's supernatural knowledge with her own mastery of understanding the thought processes of animals used in hunting, the two began their investigation into the Beast's identity by lacing several jugs of wine with Mistletoe berries and encouraging everyone at the tavern to drink it in honor of the dead, knowing that a Werewolf would have a reaction to ingesting the berries. Marcel, knowing that his best friend and Marie-Jeanne's brother Sebastien was the Beast and was seconds from being exposed, shattered a glass in his hands to distract Marie-Jeanne from this discovery.

However, Marie-Jeanne ultimately figured it out anyway, and when Sebastien threatened to kill her and everyone else if she did not allow him to flee Gévaudan in peace, she began working with Henri to develop a weapon with which to kill Sebastien and prevent him from killing any more innocent people. They eventually settled on a pike, with the intention of using the weight and force of the Beast against it; Marie-Jeanne made it even more powerful by mixing the steel of the pike's tip with Mountain Ash and Wolfsbane and forging it with her own blood under the light of a full moon.

Four years later, Marie-Jeanne was able to kill the Beast with the pike she and Henri created together. Afterward, Gévaudan's citizens punished him with damnatio memoriae, with Marie-Jeanne, Henri, and the others all destroying every vestige of his existence. Marie-Jeanne and Henri's hunting partnership eventually grew into a romantic relationship that led to the two marrying; she went on to take Henri's last name, Argent, making her brother's punishment even more effective. They continued to merge her hunting skills with his scholarly history of studying the supernatural, which ultimately began the Argent bloodline of Hunters who hunted Werewolves and other supernatural creatures.