Empress Marasiah Fel
Roan Fel planned to use a viral toxin created by his prisoner, Darth Maladi, to wipe out the population of Coruscant, which would presumably destroy Darth Krayt and the Sith as a whole at the cost of civilian lives and the lives of his men. It would later be revealed that the Sith were immune to the toxin, and would end up killing non-Sith from the Sith Empire, Galactic Alliance, and soldiers from Fel's own Empire. This was unknown to Fel when he attempted to release the toxin.
Fel's Imperial Knights - including his daughter, Marasiah Fel - rebelled against him. He swatted them away, before doing combat with Imperial Knight Antares Draco, possibly Fel's most loyal Knight. After a brief duel, Draco struck the Emperor down, and mourned over him.
Krayt was killed by Cade Skywalker, and his Sith followers scattered to the far reaches of the galaxy. Marasiah Fel became the Empress of the Fel Empire. Roan Fel was given a dignified funeral, his actions remaining a secret from the rest of the galaxy. She went on to become a part of the Galactic Federation Triumvirate, which included the New Jedi Order, the Fel Empire, and the Galactic Alliance.