Matrim Cauthon, best known as Mat, is, according to many viewers, one of the most interesting characters in Amazon's The Wheel of Time tv series. Whatever your views on the show, and the way it handled the source material, Mat stands out early on. However, towards the middle of the 8-episode first season, his character starts acting differently. Episode 6 reveals that this is due to the influence of a cursed dagger he stole. But how did this become possible, and what is the dagger?
With series that focus on outcasts and rogues - included but not limited to Netflix's Shadow and Bone - increasingly dominating the fantasy scene, there's a lot to like about Mat. In both the books and the series, Mat is a ray of mischief that brings humor to a relatively serious cast of characters. Unlike his comparatively privileged book counterpart, however, Mat is a thief in the tv show. And, like most fictional rogues, he has a backstory that explains his actions.
Both book Mat and tv show Mat have parents and sisters, but there's a tragic twist in Amazon's series, whereby the family is quite dysfunctional. His parents are in a poor physical and mental state due to alcoholism, rendering him responsible for his sister's wellbeing. Being thus used to stealing for survival adds a tragic twist to his finding the cursed dagger. While it would make sense for anyone removed from their quiet village and taken into the unknown to take a weapon they find, things become more interesting when the character is someone who's used to taking things he isn't supposed to.
So, what is the dagger and what makes it such a dangerous weapon to possess? As the books reveal, the artifact in question originates from Shadar Logoth. According to the book wiki, this once prosperous city was corrupted during the Trolloc Wars, eventually becoming dark and tainted as the evil it fought against.
Taken outside the city, the dagger can corrupt all that's good and pure. This, of course, includes its handler. It's no surprise then that Mat was horribly affected by it. In fact, the only surprise is that Mat survived over a month under its influence without irrevocably losing himself. The suspected reason for that is his ta'veren abilities and the strength that makes him a potential Dragon.
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Thankfully, in Episode 6, Moiraine arrives just in time to rescue Mat from the dagger's worst effects. If you haven't read the books and plan to, we can leave it at that. The series hasn't specified whether Mat is now completely free from the taint. However, the last scene of Episode 6, in which Mat refuses to follow his friends, might be a hint that he's still suffering the dagger's influence.
If you don't mind spoilers, what we can say is that Moiraine's power alone wasn't enough to free Mat from the dagger. While she managed to temporarily hold off its effects, Mat still had to be taken to the White Tower, where more than one person saw to him. The Aes Sedai were eventually able to wean Mat from the dagger's influence, but it took more than one spell by Moiraine. There are sufficient hints that this will be the case in the tv series. Perhaps Season 2 will shed more light on the dagger and its taint.