There's a lot of things out there that have been massively influential to me throughout my entire life, and it quite honestly never stops since there will always be something that I will eventually discover that will unexpectedly change my life. But for the purpose of this particular challenge I will be picking a singular thing that changed me during a very specific point of my life. And that thing, for me, was Harry Potter by J.K. Rowling.
I didn't really discover the Harry Potter series until after the first film came out (which we bought/rented on VHS at the time), and I didn't know what it was at first, but as the movie kept going I was like, oh, this looks interesting. I learned it was a book series that my sister had and I asked to borrow them, read them, and basically was hooked instantly from there on. But what made this life-changing for me was, during this time in my teens, it was the height of my depression. I was in a state of not really enjoying much of anything and in a constant black hole, so when I got introduced to the series it kind of opened more of that gate that was slowly start to open again for me to get back into things I enjoyed. I became engrossed with the story, wanting to escape to this magical place, and wanted to immerse myself into this world. I started to really come out from my shell bit by bit as the books and movies continued to be released, wanting to know more, being excited about where the story was going to go, going to midnight releases, etc.
So while Harry Potter obviously didn't cure my depression, it was one of the contributing factors that helped me heal along the way of getting back to myself from a dark time. And although now I view the series from a different perspective many years later as an adult, seeing the flaws and holes within the plot and being quite critical of the series as a whole, I still hold the series close to my heart for being something that helped me get through a difficult period of my life.
Honorable mentions include: Buffy the Vampire Slayer, which was a huge part of my formative years; Battlestar Galactica, which got me very interested in science fiction as a genre where previously I was more selective of it, and most recently Critical Role which introduced me to Dungeons & Dragons in a very unique way.