Great thread. This ought to be fun. I think that why should be mentioned as well.
My vote is for Charlemagne. It was he who defied Popes Adrain IV and Leo III by insisting that Filioque be added to the Creed. His motive was to seperate the Romans in the East (Constantinople) from the Romans in the West (Rome). By doing so, he could, with the help of his barbarian brethren (Goths, Lombards, Vandals,etc) more subjugate the west romans and expand his Frankish kingdom.
His efforts were rewarded when in 1014 Pope Benedict XIII, of germanic origin, inserted Filioque in the Creed at Old Rome. Within one generation, Old Rome demanded that the other catholic patriarchates add filioque as well. When they refused, Old Rome, with the support of the Franks and the “Holy Roman” Empire, excommunicated every other orthodox catholic church in the world. And that schism exists to this very day.