EverQuest

I can nearly single-handedly credit EverQuest with my career. I got my start in the ShowEQ and eqemu sphere, first building little PHP apps to manage servers and such, then reverse-engineering -- I learned x86 and then C++ all to get the lifts in Kelethin working. Hell, nearly 25 years later, any time I work on some new graphics API or game engine, I end up writing an EverQuest zone renderer.

Not my favorite game of all time, but certainly the one with the biggest impact!

Edit to add: also, huge props to that community for both humbling me and teaching me more than I could've imagined. Went from a dumbass 13 year old saying "ROT13? Isn't that some unbreakable encryption?" In the ShowEQ IRC channel because she couldn't imagine saying she didn't know something, to a competent reverse-engineer. I cannot imagine how insufferable I was haha.

Likewise. My first introduction to scripting was automating EverQuest. I learned the basics of path resolution writing a script to grind misty thicket picnics. I wrote my own HUD-style UI overlay to replace most of the default windows. And I learned about pointers and disassembly and jumps disassembling hack plugins from shady sites.