In Fate/Extra, Saber’s true identity is Nero Claudius Caesar Augustus Germanicus, the Fifth Roman Emperor. She was a notorious tyrant who oppressed all religious forces, especially Christians, and the Roman Senate during 50 to 60 AD. Her rule was so devastating and destructive that some have theorized that the Book of Revelation was written as a reaction against said oppression.
And here I thought all the Sabers were inspired from King Arthur. I’m never going to look at this red Saber the same way again. Thanks again to 4chanatic for sending this in!