Sith Lord, also known as a Lord of the Sith, was a title conferred upon individuals who followed the Sith tradition. Sith Lords drew upon the dark side of the Force, using it to gain power.
The title «Darth» was given to newly christened Sith Lords in place of their old identities. It roughly translated to «Dark Lord.»
In the years leading up to the Invasion of Naboo, the Sith Lord Darth Plagueis, who had been trained by Darth Tenebrous, was killed by his apprentice Darth Sidious, who also took on his own apprentice, Darth Maul. Sidious’ alter ego Sheev Palpatine became the senator of Naboo in order to inflitrate, deceive and eventually destroy the Jedi and Galactic Republic. Sidious planted the seeds for what would become the Confederacy of Independent Systems by forming an alliance with the Trade Federation, a corporation led by Viceroy Nute Gunray and Settlement Officer Rune Haako. Sidious convinced the Trade Federation to use their army of battle droids to blockade and invade the peaceful planet of Naboo, in order to unseat Supreme Chancellor Finis Valorum and have Palpatine become the Chancellor. The invasion failed and Maul was seemingly killed by Obi-Wan Kenobi, but Palpatine was elected as Supreme Chancellor of the Galactic Republic.
The Sith then resurfaced ten years later. Darth Tyranus, Sidious’ apprentice, met with Viceroy Gunray, and other influential magnates, on Geonosis. They supported the Confederacy of Independent Systems, leading to the start of the Clone Wars against the Republic. A number of other Sith were also active during the war, such as Sidious’ former apprentice Maul, Tyranus’ first apprentice Asajj Ventress, and Tyranus’ second apprentice and Maul’s brother Savage Opress. Due to Sidious being both Chancellor of the Republic and Tyranus’ master, he was able to manipulate both sides of the war, while deceiving both sides, leading to Order 66, the defeat of the Confederacy, and the establishment of the Galactic Empire.
Not long after Tyranus was sacrificed and betrayed by Sidious, Jedi Knight Anakin Skywalker turned to the dark side and became Sidious’ new apprentice, receiving the name «Vader» which was preceded by the moniker Darth, roughly translated as «Dark Lord.» With the Great Jedi Purge in effect and Darth Vader at his side, Sidious consolidated his power over the galaxy as the self-proclaimed Galactic Emperor.
Years into the Imperial Era, Grand Moff Wilhuff Tarkin and Vader oversaw the deployment of the Death Star battle station. However, the Rebel Alliance destroyed it along with Tarkin during the Battle of Yavin. The Rebels then continued to defy Imperial rule for a further five years, leading to the Battle of Endor with the destruction of the DS-2 Death Star II Mobile Battle Station and both Sith Lords. As the battle turned in the Alliance’s favor, Vader sacrificed his life by killing his master in order to protect his son, Luke Skywalker, thereby renouncing the dark side, fulfilling his role as the Chosen One, and dying as Anakin Skywalker.