Darth Maul is introduced as a Sith Lord in Star Wars: Episode I The Phantom Menace, yet whether his Lordship was deserved is questionable. While the Jedi refer to themselves as Knights who serve the will of the Force, the Galactic Republic, and innocents of the galaxy, their ancient enemies use the title of Lord instead. The first Sith may have been fallen Jedi, but the Sith Order soon developed its own distinct culture from the Jedi. Sith are Lords because they rule (or seek to rule) the dark side of the Force, the galaxy, and its beings.

https://screenrant.com/star-wars-darth-maul-sith-lord-worthy/