I'm a fan of strategy RPGs. But I'm sure there are varying stories. Especially for the formula and defining games. But I think in a lot of cases its probably something like Fire Emblem as the first, probably Tactics Ogre for the formula and Final Fantasy Tactics to define the genre, which went on to even more popularity when Disgaea got ahold of it

But for me, since I never played Fire Emblem, or any early strategy games, as I'm pretty sure none of them were released in America (pretty sure Warsong was like the third game in the Langrisser series or something like that. Its been a while since I read a history on it) if I recall correctly, Shining Force was actually the first strategy RPG in America. Or at least close to it. But regardless, it was my first foray into the experience. So at the very least, that's the formula layer for me. I'm still looking for my definer in the genre, as FFT didn't appeal to me. Too convoluted. I'd love to say Disgaea, 'cause that had a great story and characters, and the combat wasn't so complex. But it did add needlessly more complex formulas with the stupid colored tile crap. I hate when SRPGs do that kinda stuff. And of the simpler tactical games, none of them have the fun and charm of the ol' Force games. Though this may not even be meant to be personal opinion anyway :}

Point and click adventure games would be another interesting category to look at. Though unfortunately I'm only on my break at work, and quickly skimming Wikipedia for the first graphical point-and-click adventure game is a little hard to discern. As they started out text based, then slowly evolved graphics. Phooey. Good topic though