Mustafar was a volcanic planet that was mined by the CIS during the Clone Wars. The Separatists set up a state-of-the-art facility there to protect its leaders from the wrath of the Republic, although they were eventually hunted down, and destroyed by Anakin Skywalker anyway.
Mustafar was the planet that Obi-wan fought Anakin and defeated him.
At the time of the Clone Wars, the Techno Union had owned Mustafar since its (re)discovery c. 300 BBY, harvesting minerals and energy from the 800-degree-hot lava. It was comparatively cool compared to most other lava due to the unusual mineral allotropes that became molten at a lower temperature. Regardless, the lava could only safely be mined when a repulsor field was placed to repress any eruptions and deflect heat away from those harvesting it.
The main Separatist stronghold was located in a massive industrial complex located on a fiery cliff bracketed by two huge lava flows. Collection arms mined lava from the area, while durable industrial droids worked further afield. Within this facility lay a Separatist command center, one of the most secure bunkers in the galaxy.
During the early years of the war, Palpatine, in his guise as Darth Sidious, tasked the Duros bounty hunter Cad Bane with kidnapping Force-sensitive children and taking them to a secure facility on the planet, where he could turn them into a cadre of Force-wielding spies. The plot was scuttled by Anakin Skywalker and his Padawan, Ahsoka Tano.
Toward the end of the Clone Wars, Palpatine would continue to have a vested interest in the planet, ordering General Grievous to move the Separatist Council there near the end of the war, apparently for their own safety, but in reality to gather them together so that Anakin, newly anointed by the Sith Lord as Darth Vader, could kill them all and deactivate the droid armies, bringing about the end of the war. Shortly afterwards, the duel between Obi-Wan Kenobi and Darth Vader would also take place on the lava planet. During the duel, the controls to the mining complex were destroyed and the repulsor fields dropped, allowing the violent lava eruptions to overwhelm the complex. Vader suffered grievous injuries including the loss of his remaining limbs and the searing of his lungs when he attempted to jump to higher ground from a platform on the lava river, only to be immobilized by Kenobi. He was later rescued by Emperor Palpatine, who brought him back to Coruscant where he was rebuilt into the feared cyborg executor of the Emperor at the Emperor Palpatine Surgical Reconstruction Center. It was also on this planet, immediately prior to the Kenobi/Vader battle, that Lord Vader, who unbeknownst to Padmé Amidala was no longer the man she had married, Force-choked the pregnant Senator of Naboo into unconsciousness. This would eventually add to the causes of her death, along with the loss of will she suffered alongside her broken heart.
Galactic Civil WarEdit
The mission was successful as the duo narrowly escaped from Imperial soldiers and a squadron of TIE Fighters.
After the destruction of the first Death Star, it was rumored that several would-be Jedi found their way to the legendary world of Mustafar, and were apparently guided on their path to Knighthood by the spectral form of Obi-Wan Kenobi. A disturbance caused by a gathering of dark side energy drew Kenobi's spirit to the planet. Other explorers at the time apparently encountered the ancient assassin droid HK-47 along with an ancient Hammerhead-class ship.