Mission to Mustafar/Legends

The Mission to Mustafar at the end of the Clone Wars was Darth Vader's mission to kill all the leaders of the Confederacy of Independent Systems. While Vader was successful in carrying out his mission, his old master Obi-Wan Kenobi was there to challenge him after he had carried out his orders. The duel raged on until Vader's three natural limbs were severed by Kenobi's lightsaber when Vader tried to make a leap over Obi-Wan. This incident was what forced Vader to wear a respirator and full body suit for the rest of his life.