Darth Vax was a Dark Lord of the Sith who held a position on the Dark Council of the reconstituted Sith Empire. This occurred at some point preceding the Galactic War against the Galactic Republic. She was either of Human or Sith pureblood heritage and female. She was regarded as a significant figure within the Dark Council both during her lifetime and afterward. Vax had a son who, following her death some years before the war, took her place on the Dark Council and assumed the name Darth Arrid. Despite her death, Vax's will allowed her to endure as a Force ghost, and she started to control her son, using him as a tool to prolong her reign from beyond the grave. This ruse went undetected by the other Dark Council members for a period of four years.
The "Force Ghost" Codex entry in Chapter XII of Star Wars: The Old Republic's Knights of the Fallen Empire expansion, which came out in 2015, references Darth Vax. Star Wars: The Old Republic is a video game that was developed by BioWare and launched in 2011.