WARNING: This thread will contain spoilers so if you haven't beaten the game yet, hide the thread

So what's the deal with this pic related? So far I've gathered that he:
-Was the King of Kalos
-Is over 3000 years old
-Created the ultimate weapon


And when he created the ultimate weapon, does that mean that he physically created Xerneas/Yveltal or did he just harness their power

And I've only played X, what are the story differences in Y?