Kel Desmin was a Zabrak Jedi-turned-Sith who brought the Jedi to their knees.
Discovery and fall
As a young child on Iridonia, Jedi Master Herron found Kel, discovering his Force-sensitivity, and took him to the Jedi Temple on Coruscant. Kel went to the archives in his spare time to find out more about the galaxy, eventually going against the will of the council: leaving Coruscant to explore the galaxy.
Kel eventually found a secret Sith base on Phaldar. He went back to the Jedi Temple on Coruscant, but was not allowed to leave Coruscant without Jedi supervision. Soon, Kel was made a Jedi Knight by the Jedi Council. He went to Herron's quarters, but spotted Herron talking to a hologram of the Dark Lord of the Sith, Darth Thun. An enraged Kel ignited his blue lightsaber and lashed at his former master, but Herron ignited his brown lightsaber and a duel began.
Herron lashed at Kel with his lightsaber, but Kel cut off Herron's left hand then stabbed him with his own lightsaber, kicking him out of the window. As the Jedi arrived, they told Kel that Herron was a double-agent and because of his murder, Kel would be exiled. Enraged, Kel embraced his anger and his hate and lashed Force lightning at them, killing them both. Kel then made his exit.
Training under Lord Thun
Kel eventually went to the Sith fortress on Ryloth to learn the ways of the Sith. As he arrived in the fortress, Thun said he would test Desmin in battle before becoming his apprentice. He placed Kel in an arena, where a door opened and two mutated rancors came out. Desmin made quick work, throwing them into each other and into a wall. Darth Thun eventually took Kel Desmin as his apprentice and they both went to Geonosis to assassinate Archduke Julo the Lesser. Kel saw an opportunity to kill his master so as they entered the palace. He stabbed a lightsaber through his master's heart, killing him, Kel then killed Archduke Julo and reorganized Thun's Empire into Kel Desmin's Sith Empire.
The Dreaded Talon
Kel Desmin eventually found a battered cruiser lying above Cato Neimoidia and found a huge amount of dark side energy. He took control of the ship and placed it as his fortress, using it in his mission to Dorin. He took a shuttle down to Dorin and was greeted by Kel Dor troopers. Desmin killed them then moved into the palace. As he slaughtered his way to the throne room, he noticed his breath mask had been penetrated. He quickly moved and found the Kel Dor king. He killed the king and retreated into his shuttle. As he arrived back on the Dreaded Talon, he weakened and began to die, but to save his life, he drained the life out of a Sith warrior, killing the warrior but saving himself.
Battle of Mustafar
Kel Desmin's Empire went into its last battle against the Republic on Mustafar. As the battle raged on, Kel dueled and killed over fifty Jedi. Eventually caught by surprise, Kel was stabbed by an unknown Jedi Padawan. He fell to the ground, mortally wounded, and was taken to his tomb on Korriban.