The ultimate of all ultimate Sith lords. He was the twin brother of Palpatine aka Darth sidious. He was so powerful with unimaginable power from the dark side. He remained in hiding secretly watching over Palpatine ruling the empire. Even Palpatine would never dare to challenge his twin. After the fall of the empire, Darth Ratzinger flet to a very far away unknown planet full of humans, called the Earth. There he tricked the earthlings with his god level powers and became religious leader, under the alias, Pope Benedict XVI and rules over them. At his prime before the Empire's beginning all Jedi and Sith feared him, even Yoda himself.
Darth Ratzinger is the most OP Sith lord. He's an identical twin brother of Palpatine, but stronger that all Jedi and sith in the galaxy fears him.