What is the most defining strategy/4X games in your life and why?

Théa The Awakening, that game combined the 4x base design with a rpg system and a really interesting card-system fight, + a craft system really funny and interesting to use :)
Moreover this game have a background who is worth to be called a scenario (still not really finished yet), which doesn t really exist in most of 4x game (none in sid meier civ / galactic civ, not really interesting in endless legend) .
AND going in harder difficulty isn t totally broken like in civ (civ 5 hardest difficulty opponent start with 3 settlers with capital city full build + reasearch first era already done + alreadey tile improvment done + army already built). Here it s a matter your civilian / soldier are fewer, less equiped, ennemy are more aggressive, use stronger strategies and basic ressources may not be close to your village at the start, and bigger map who makes the highest quality ressources REALLY HARD to reach.
Note that i managed win this game at hardest difficulty :D (True God of Thea).

But if this game could have an interesting background, which can evolve with players actions by "events", that would be a great add-on to the 4x system :)

Didn't notice that this was a topic only reserved to oldster :), maybe because i am less than 30 that i can't talk about everything you mentioned ;)
But you're right that's a bit too early for TTW.

I think the first true strategy game I played was Age of Empires (yes, the first game in the series). The idea of being able to manage an entire nation (if you can call it as much) grasped me in a way that not many games after have. And it came with an editor as well! Needless to say, much time was spent endlessly placing units and buildings in a way that would lead to the most awesome battles.

After that, the first Command and Conquer game was up and this time it was the way the game introduced it's mechanics (read: units and buildings) and awesome cinematics (it was the nineties) that opened a whole new world. I still think fondly of the Obelisk of light, and I wasted many hours drawing up base layouts on paper with squares.

Next up were not so interesting but nonetheless engaging entries, such as Starcraft, Warcraft II, Total Annihilation, Dungeon Keeper II and Dark Reign (2, I think). I also think "Beasts and Bumpkins" deserves a reference, because it was a fantastic game, and one that has not really gotten a sequel.

Some time later I was introduced to my first 4x game, Heroes of Might and Magic III and it was love at first sight. It was with Disciples II that my love for the turn based strategy kicked in and although it might not be a true 4x game, I think this is the game of all the previous listed games I played the most.

To be frank, this is a mean question to ask. I can't pick a game of the hundreds I've played and say 'this is the one I liked most'. But it was a nice trip down memory lane...