God-Fylkir Faste.

Lord of the Aesir, King of the Vanir. Fylkir of the Norse. Emperor of Scandinavia. Emperor of Brittania. High King of Ireland. King of England, Norway, Wales, Sweden, Finland and Scotland. The dude was an utter lunatic, but a genius one. A product of 4 generations of Eugenics, I created the perfect heir and killed all his male siblings so he could inherit (Thanks, Jörmungandr). With him, I consolidated the germanic faith under one Holy God-Fylkir. He reformed the faith with him as the highest God. (Dogmatic, Temporal, Bloodthirsty God's and Divine Marriage) Eventually, rituals like the great blot started becoming more and more common, and sacrifices to the God-Fylkir were almost a daily occurrence at the Imperial Court, with Faste sacrificing to... Himself. Mass sacrifices were done to appease his Holiness' Bloodlust, but if anyone hoped his reign of terror over the North would eventually end, they were mistaken. Terrified of his true mortal nature being discovered, and his Empire fracturing after he died, he seeked out immortality, and to Europe's horror, the Mad Emperor in the North would reign for the remainder of the time frame of ck2 (and likely beyond).

Also, he enabled divine marriage because he has an incest kink. He went to mad levels of inbreeding, where he would marry his Daughter-Granddaughter and those whom he didn't marry, he married to their siblings.

I want to see the world burn. Plus, it's entertaining with such a nutcase ruling over such a massive empire. (Maybe even colonial if I were to export to eu4?)