|There can be only one...|
Fighting Fantasy! I discovered these gamebooks in the school library at around the age of nine, when I lived in Matamata, which is now the home of Hobbiton. Warlock of Firetop Mountain was the first and it was brand new! Then (over the next few years) came other books, including The Citadel of Chaos, The Forest of Doom, City of Thieves, Deathtrap Dungeon (my favourite for some reason), Island of the Lizard King, Scorpion Swamp and Caverns of the Snow Witch.
These were the years before my first game of D&D. Deathtrap Dungeon stands out because it was a 'Trail of Champions', set in a deadly labyrinth of traps and monsters. Not only did you have to survive against those odds, you also had to compete against five other contestants: "There can be only one winner in the Trail of Champions."
All for the glory and your weight in gold!
The first non-D&D RPG after playing Dungeons & Dragons? Dragon Warriors.