Darth Bane is the Sith Lord who created The Law of Two, which states that only two Siths can exist, one being a master and the other an apprentice. Also created the new Sith Order which would overthrow the Jedi Order in the future.
Darth Vitiate, as he was known to the Old Sith Empire, was the longest-reigning Dark Lord of the Sith, wiping out an entire planet and absorbing the powers of various Sith Lords. Although considered to be immortal, he passed away millenniums after his birth.
Darth Sidious, known as Sheev Palpatine amongst the people unaware of his true nature, is a Sith Lord who was the former mentor of Darth Maul and the master of Darth Vader. He is best known for overthrowing the Jedi Order as the last reigning Dark Lord of the Sith under Darth Bane's Rule of Two.
Darth Plagueis, also known as Darth Plagueis the Wise, might not be known for his ability to harness the Force nor his skill with the lightsaber but his knowledge of using the Force to create life, and preventing it, has become a legend amongst the ranks of the Sith Order.
Marka Ragnos was considered to be the best duelist in the entire Star Wars universe, besting every opponent in single combat. Although his control of the Force wasn't the best, he still reigned supreme for plenty of years.
Darth Maul is a character from the Star Wars Universe. He is a Dathomirian Sith who was the apprentice of Darth Sidious. Darth Maul is also known for besting Qui-Gon Jinn whilst fighting him and his apprentice Obi-Wan Kenobi, although he was ultimately killed by the latter.