In 19 BBY, Darth Sidious, the Dark Lord of the Sith and Supreme Chancellor of the Galactic Republic, sent his new apprentice, Darth Vader on a mission to kill the remaining members of the Separatist Council on the volcanic planet Mustafar. The Council, consisting of the surviving top members of the Confederacy of Independent Systems, was a loose end in Sidious's plot to gain control of the Republic and mold it into the galaxy's first empire.
Vader willfully carried out the slaughter after trapping the council in their war room, killing each council member one by one. The bloodbath ended with the death of Nute Gunray, the Viceroy of the Trade Federation and one of the most influential members of the Council. As the violence came to an end, Vader received the order to send a shut down signal to all battle droids part of the Separatist Droid Army, ending the Clone Wars that had spread across the galaxy for the past three years. This, coupled with the Chancellor's Declaration of a New Order at the Galactic Senate, secured Sidious's position as the Galactic Emperor of the New Order.
Before Vader was able to leave the planet, he was intercepted by his wife, Senator Padmé Amidala of Naboo, who inadvertently smuggled Vader's old master, Obi-Wan Kenobi, to Mustafar. The ensuing confusion caused Vader to accidentally wound Amidala in his rage. An epic duel between the two former companions ensued, leaving Vader heavily wounded and burned.