Dungeons and Dragons
I played Advanced Dungeons & Dragons for several years both as a Player Character and as a Dungeon Master. The influence of AD&D on my writing cannot be overstated. As a player I learned that the part of the game that was the most fun was actually playing the character, becoming the character, interacting with the fictional world that the Dungeon Master created not as I would as myself but as my character would based on their personality, knowledge, and background. You could play the game by just knowing the mechanics, like what roll on a twenty sided die you needed to hit armor class two with a long sword, but it was far more fun if you had a history and unique personality for your character and allowed that character to emerge. As a Dungeon Master AD&D helped me, actually forced me to develop a believable world with which players could interact and an interesting story for them to become a part of. The first AD&D character I ever rolled up features prominently in my Warden novels (although the spelling of the name has changed) and a few others are there too with or without name changes. If any of the folks in my old AD&D group (The Mutants of the Round Table) ever read these (assuming they’re ever published) please let me know if you recognize them. I’d love to hear from you.