he was born as a sith pured blood with dark eyes, OP read the Revan book
The Sith Emperor was a Dark Lord of the Sith who reconstituted the Sith Empire after the Great Hyperspace War and went on to rule for more than a millennium.
Born in 5,113 BBY as Tenebrae, the illegitimate son of Lord Dramath of Medriaas and a poor farm woman, the child who eventually became the Emperor killed his own father at the age of ten and was granted the title of Lord Vitiate by the current Dark Lord Marka Ragnos three years later.
Vitiate renamed his world Nathema and ruled for the next hundred years, during which he witnessed the destruction of the Sith Empire at the hands of the Galactic Republic in the Great Hyperspace War, as he did not participate.
He then summoned the remaining Sith Lords to Nathema to cast a powerful ritual in order to save themselves from the Jedi.