Syrio Forel
Arya Stark would not be the complete badass she is were it not for Syrio Forel, her sword-fighting teacher. The master Braavosi “water dancer” was the first to mold Arya into the deadly fighter she’d become. Plus, he instructed her in the proper way to use her sword, Needle (beyond “stick them with the pointy end”). And that’s something you don’t forget.