I thought it was a chosen thing, as I could think of Sith Lords both with and without, but I wanted to corroborate so I checked Wookieepedia: Many Sith Lords chose to add “Darth” to their name, so much so that the word is considered synonymous with the dark side of the Force in some circles. It was also taken to signify giving up one’s old life. Such examples are Anakin Skywalker becoming Darth Vader, or Jacen Solo becoming Darth Caedus. But the origins of the word are uncertain. It is often thought that “Darth” is merely a contraction of the title “Dark Lord of the Sith”, but there are theories that suggest a deeper interpretation.
I don’t think it’s particularly well-defined, however.
My personal take would be that it’s an honorific bestowed when the character becomes the Sith equivalent of a knight. As an apprentice, they have whatever name, and then when they graduate and become independent, they take on a Darth name.
Darth Maul went through Hell and back before the Phantom Menace, so that’s how he already had the title. I second the experience and achievement requirement. Maybe Force Rating 2 minimum, like Jedi Knight?
I’d guess the rules are probably different in the Rule of Two era, like how Ventress (arguably just a Sith Assassin, but could be called an apprentice) didn’t have a Darth name, but Maul did.
So like maybe in the Old Republic, they got it when they “graduated” but in the Rule of Two era, they were considered to be past the point of acolytes already and so started with that name.
Does anyone remember at what point Sheev Palpatine became Darth Sidious?
It was only explained in the Bane trilogy. It was a title worn by the original sith iirc. However in the books they casted away that title when they made the Brotherhood of Sith to represent the cooperation and no more betrayal policy between the dark side users. Bane uncovered the old knowledge, annihilated the Dark Brotherhood and started the rule of two. One usually gets it, when he dedicates his life to the rule of two.
The SWTOR or KOTOR in that manner is technically before that time, but they are really not consistent in this regard. They are usually using the name far and wide.
TLDR: As always, lore is contradictory and use it however you wish :D
In SWOTOR only the Sith Inquisitor becomes a Darth when she / he finishes her / his storyline and enter the Sith Council (or is it named Dark Council ? It’s been 7 or 8 years since I did it). Then you earn the title in game and can put it in front of your character name.
The other Sith storyline : the Sith Warrior doesn’t become a Darth even after becoming the Fury of the Emperor.