The name Darth Plagueis is mentioned a few times by Sheev Palpatine in Revenge of the Sith in reference to his old master's most famous obsession with cheating death. Palpatine wasn't entirely honest with Anakin Skywalker about Plagueis, however, and left out the part where he was killed by his apprentice before he could complete his research.
Plagueis was famous for his detailed knowledge of the Force partly through his extensive scientific knowledge and often gruesome experimentation as opposed to being the strongest or most powerful Sith Lord. He taught his apprentice to strictly follow the Rule of Two, which was the main reason his apprentice murdered him.
Malak was a student of Revan, another infamous Sith Lord of considerable power, and like his Master he was also formerly a Jedi Knight. Where Revan appears in the lore, whether it's in games, comics, or cartoons, Malak isn't too far away.
Known by the nickname Squint when he was a Jedi, the metal prosthesis he wears on his face covers his missing lower jaw, which was removed by a lightsaber swipe from Revan during a time when things were complicated between them. Revan eventually redeemed himself and rejoined the Jedi by turning on Darth Malak and killing him, giving the Republic a decisive victory in the Jedi Civil War.
Naga Sadow was a Sith Lord from a time that was thousands of years before the modern films or even the setting of the Star Wars: The Old Republic MMORPG. He's one of the main antagonists of the Qel-Droma Epics, the stories that chronicle the Unification Wars and the reign of Empress Teta, and is recognized as one of the most powerful Sith Lords in early history.
By the time of the Unification Wars, Naga Sadow was already ancient, and many of his accomplishments are lost to time. The Great Temple on Yavin 4 is believed to have been built by Massassi warriors who worshipped Naga Sadow as a god, and his effigy can be found carved into several locations on the Sith planet of Exegol.
Also known as Count Dooku, Darth Tyranus began as a Jedi Master but eventually left the Jedi Order and secretly became the apprentice of a Sith Lord, Darth Sidious. The Jedi Order didn't suspect him until it was too late because of his history with them, and Anakin killed Tyranus before his secrets could be revealed.
Tyranus was an orphan that had been taken in by the Order and trained by Master Yoda himself. It was the corruption of the Senate that shattered his ideals and drove him to leave the Jedi Order and act as a political and trade emissary instead. At least, that was the cover story. The reality was that he had embraced the Dark Side and become one of the strongest Sith Lords in the galaxy.
By Andeddu's flames, an enraged student of the Dark Side might scream before their final attack, and this expression comes from the Sith Lord Darth Andeddu. This character dates so far back in the lore that he might have been the first to carry the Darth title.
Another one of his titles was Immortal God-King of Prakith. That was the planet he fled to when he was betrayed and overthrown by his own followers on Korriban, and where he ruled comfortably as a deity for some time. Unlike other Sith Lords, Andeddu did figure out a way to cheat death by putting his essence inside a Holocron before his body expired.
Darth Shaa first made a name for herself when she rescued Momin, a force-sensitive sculptor from his imprisonment, and made him her apprentice. Despite the fact that Shaa lived before the Rule of Two, Momin still killed her eventually.
Shaa was a master at wielding dual-light sabers before it was cool, and was lethal with her melee weapon technique along with her Force powers. Momin would eventually use her teachings and resources to craft a deadly superweapon that the Jedi had to find and destroy, a skill that made her one of the most powerful Sith.
In the years preceding the rise of Darth Plagueis and his apprentice, Darth Maul, Exar Kun was the go-to guy in the galaxy when it came to the Dark Side. He began as a Jedi Knight but was always known for being quick to anger. When he came across the tomb of the Sith Lord Freedon Nadd, the spirit of the former Dark Lord sent him to Korriban, and by the time Exar Kun reached the home planet of the Sith the Dark Side had consumed him.
After he became a Dark Lord of the Sith, he took on an apprentice, his former rival Ulic Qel-Droma, and together they started the Great Sith War. At the moment of his defeat, Exar Kun performed a ritual that was intended to free his spirit to roam freely in the cosmos, but instead, his essence was trapped on Yavin 4 and remained there until it was exposed and banished by Luke Skywalker and his students.
The second and last apprentice of Darth Sidious, the master intended to swap out Vader for his even more powerful son, Luke Skywalker, similar to the way he had replaced Dooku with Anakin. This didn't go as planned, however, when Vader resisted and turned on his master instead.
As a servant of the Empire and his Sith Lord, Darth Vader was essentially a galactic thug with deadly Force powers and a massive army at his beck and call. He was thought to be the last being in the galaxy with Force powers for several decades after hunting down and killing the remaining Jedi Masters and Knights — that was until his master was revealed, and his children were brought out of hiding.
A former Jedi Master and one of the most controversial names in the Star Wars canon, the Jedi formerly known as Kreia sought to understand the Force on a deeper level and resisted the absolute teachings of both the Jedi and the Sith. Revan, one of her most successful and infamous students, would continue her tradition of giving equal weight to both the Light and Dark sides of the Force.
As a Sith Lord, Traya led an Order of her own, but as the chaos between the Sith and Jedi grew, she decided that neither side deserved to dominate the galaxy and that the Force robbed sentient beings of their individuality. She was eventually defeated by her closest pupil, Meetra Surik, who went on to join forces with another former student of Traya, Revan.
An ancient Sith Lord that appears frequently in the lore, he's been in a few of the BioWare and LucasArts games and is famous for being an early example of a Jedi Knight who turned to the Dark Side. During the Jedi Civil War and the Mandalorian Wars, he often played both sides.
Also known as Revan the Butcher, the modern legions in the Sith Eternal army name their units after him to honor his bloodlust and ferocity. Very little is known about exactly where he came from other than somewhere in the Outer Rim territories. The mask that become synonymous with his identity was Mandalorian, taken from an enemy's body when he was fighting for the Galactic Empire.
Darth Phobos spent most of her early years killing her fellow Sith in an attempt to gain more power. She's mentioned frequently in the lore but so far has only made an appearance in the video game Star Wars: The Force Unleashed.
This deadly Sith Lord earned the nickname "The Hidden Fear" and boldly claimed she was a nightmare to her peers. The Cult of Darth Phobos worshipped her as a god for hundreds of years even after a cooperative army of Sith and Jedi killed her.