Darth Perfidious was a Human male Sith Lord of the Sith Empire during the Great Galactic War. He was born under the name of Benla "Ben" Vidar within Republic space on Corellia, and raised by his mother and father. While still a young adult at the age of 20, Ben killed a Zabrak male, by way of Force Strangulation, for cheating at a game of Sabacc which Ben was about to win. The authorities of Corellia, upon learning of the manner of which the Zabrak has died, hunted Ben for not only murder, but for use of the Dark Side of the Force as well. Ben was able to evade the authorities for 3 days until he managed to escape the planet via cargo shipments being sent off-world. At the same time as this happened, the Great War between the Sith Empire and Galactic Republic had commenced.
The cargo shipment traveled far into the Outer Rim until it landed on the Imperial controlled planet of Karideph in the Minos Cluster. From there, seeing as he had already committed murder and he couldn't go back to Corellia due to the authorities, Benla joined the Sith Empire's Navy. Over the course of five years, Benla had become a skilled strategist and excellent leader, having successfully lead his troops to victory in multiple battles against the Republic. Soon, word of Benla's talent with the Force spread throughout the ranks and was soon recognized by the Sith Lords as a possible trainee in the Dark Side. They brought Benla to the Imperial capital of Dromund Kaas, where he became a Sith Warrior and revered captain of the Imperial Military, serving under Darth Malgus himself.
Benla quickly showed disdain for his leaders and fellow Sith Lords, one of them being his Master Dargar Nell, seeing them as inferior strategists for following hastily planned maneuvers that often led the Sith Military into horrid loses against the Galactic Republic, including the disastrous attacks on Bothawui and Alderaan. Fed up with the needless loses at the hands of the incompetent commanders and captains, Benla slaughtered his master and the eight leaders, taking on the mantle of Head Strategist and Sith Lord. News of his act reached the ears of Darth Malgus and the other Sith Lords. They believed Benla to be a traitor, thinking he had no idea what he had just done by killing those commanders and captains, and planned to court marshal him. Enraged by their accusations, Benla persisted that he was doing this for the betterment of the Empire and that he would prove his superior intellect by overseeing the Sith's next victorious conquest of the Republic capital of Coruscant. Despite the demeaning allegations the Sith had placed on him about being a traitor, Benla cast aside his birth name and took on the title of Darth Perfidious, ironically meaning treacherous.
In 3653 BBY, The Sacking of Coruscant went off without a hitch, just as Darth Perfidious had expected. Though Darth Malgus lead the strike force that invaded the Jedi Temple (of which Perfidious co-lead, killing nearly seventeen Jedi himself) and was given the credit for the victory. Darth Perfidious, however, was commended for his brilliant planning by Darth Angral himself in a private meeting. This suited the young Sith Lord just fine, knowing that his abilities had greatly surpassed everyone's expectations.
During the Cold War years, at the age of forty-eight, Darth Perfidious decided it would be prudent if he trained his own apprentice, passing on his skills to a worthy successor so his legacy could live on. After three failed attempts at finding a suitable student in the Sith academies, Perfidious traveled to the Outer Rim world of Pantora. There he searched among the four young teenagers reportedly to be well attuned with the Force. Fortunately, one out of the four completed Perfidious' initial challenges. The champion of these challenges was a female Pantoran named Lah'ri. Perfidious took her as his apprentice, and over the years, she became a Sith Warrior of sheer tenacity, a stunning duelist, and wielding a mind as cunning as her Master.
Following news of Darth Malgus' defeat on the space station orbiting Illum, Darth Perfidious and his apprentice Darth Lah'ri went out to destroy any Republic forces left in the Outer Rim. After a fair few successful skirmishes, Darth Perfidious' Harrower-class Dreadnought, The Deceiver, came under assault by a large surprising force of ten Republic battle cruisers. Though the attack failed against Perfidious' ship's superior might, the Dark Lord was injured in his right leg with shrapnel from a nearby explosion. He was healed with Bacta, but the wound was so severe that it left him with a twinge in his leg when he walked. After the battle, and on their way back to the Core, Perfidious' apprentice decided it was time his usefulness had come to an end. She challenged her Master to a lightsaber duel. Darth Perfidious proved to be the more powerful in the Force, but not by much. His apprentice had learned well. He was able to keep Darth Lah'ri at bay for more than three hours until she took notice of his scarred leg becoming more agitated as their battle went on. At her first and only chance to defeat her Master, Lah'ri took advantage of his limited mobility, broke through his defenses and plunged her blade into his injured thigh, proceeding to decapitate the Sith Lord in one savage strike, ending his life.