Panda
Metal head
Alex, Napoleon and Ragnar have lately been pains in my *******s. 

In my games, nobody is a bigger backstabber than me. I will usually even demand tribute, then declare war on the same turn whether they pay me the tribute or not. I make peace deals just to regroup and reinvade in 10 turns. I am most likely to attack friendly or pleased relations because they are often either my neighbors or the guy in the lead.
So yup, I am the biggest backstabber in my games.
wang kon attacked me when he was on pleased terms with me, it was a late war so maybe he was just trying to prevent my domination victory, over the course of the game i had given him plenty of techs and ALWAYS accepted his demands... he was on pleased,
10 turns later he had been crushed, and was a powerful vassal ally of mine to finish off my win, lol!