Marka Ragnos is a Dark Lord of the Sith of the first Sith Empire, a hybrid of human and Sith-species ancestry, who held the title for over a century before his death around 5000 BBY. He appears in Dark Horse's Tales of the Jedi line.
Rule by attrition
Ragnos took the title by defeating the Sith Lord Simus and held it not through any single feat but by outlasting everyone — setting rivals against each other and making sure no coalition ever formed. The comics present him as the Sith Empire's high-water mark precisely because nothing happened during his reign: a hundred years of stable tyranny.
The funeral
His most consequential scene is his own memorial, where Naga Sadow and Ludo Kressh begin the fight over the succession that leads directly into the Great Hyperspace War and the collapse of the empire. Ragnos appears as an apparition to tell them both to stop, and neither does.
A spirit in a tomb
He persists afterwards as a spirit bound to his tomb in the Valley of the Dark Lords on Korriban, a role the later games and comics reuse repeatedly. The Valley itself — a necropolis of Sith Lords who each left something behind — is one of the Legends shelf's most durable inventions.
Canon status
Star Wars Legends. Ragnos and the first Sith Empire have no counterpart in current canon.