The Vithian king known as Sedris was human once. He ruled Vithia as one of its wisest kings in the early years after the plane's separation from Alara. No one knows what triggered him to give in. It's unlikely that anyone alive today even remembers that he once sat on the throne in Vithia's capital.
For you see, Sedris was seduced by evil forces. Demons, unable to assault the kingdom directly, instead tempted its leader with dreams of power, and he fell. Sedris handed the lives of thousands of humans in his kingdom to demons in exchange for the power and unlife of a lich. As his body died, Sedris's mind flooded with dark power. His humanity fell away. The transformation was complete - Vithia's king was now a lich.
In the end, Sedris massacred all of his family and close advisors to fuel the bloody ritual that would ensure the continuation of his consciousness into unlife. That's what happens when you mess with demonic pacts, folks. The knights and paladins of the realm, astonished and unable to assassinate or thwart him, perished with the old word for "traitor"—grixis—on their tongues.
He bids his minions rise from their graves to their knees.
"The future is a snake, devouring your life backwards through time. And when you die, believe me, it doesn't stop feeding." -Sedris, the Traitor King (Shadowfeed)
"This is going to hurt a lot, but on the bright side, you'll be dead soon." -Sedris, the Traitor King (Lightning Talons)
"Too wary to charge, too prudent to serve. Not anymore." -Sedris, the Traitor King (Sewn-Eye Drake)
"The meek inherit nothing." -Sedris, the Traitor King (Wretched Banquet)