During the age of the Old Republic, a Force-sensitive being, affiliated with the Jedi Order, began to delve into the forbidden knowledge of the dark side of the Force. This individual came to the conclusion that a Jedi's true power lay in harnessing the dark side, a stark contrast to the light side's emphasis on contemplation and inaction. The Jedi High Council, deeply disturbed by these beliefs, made the decision to banish him from their ranks. This fallen Jedi attracted a following, and their collective actions ultimately resulted in the creation of the Sith, an order that emerged during the Hundred-Year Darkness. The Sith became the Jedi Order's age-old adversaries. As time passed, the identity of the Sith Order's originator was erased from historical records.
The initial mention of this renegade Jedi within canon occurred in the Encyclopedia entry about the Sith on the StarWars.com website. According to The Odyssey of Star Wars: An Epic Poem, a 2021 book authored by Jack Mitchell, the Sith Lord Darth Sidious paid tribute to the founder by commissioning a statue crafted from the most durable crystal available. This statue was displayed alongside another depicting the Sith Lord Darth Bane, the architect of the Rule of Two Sith reformation, aboard the DS-2 Death Star II Mobile Battle Station. Mitchell clarified that these statues should not be considered strictly "canonical" or "anti-canonical," as they are absent from Star Wars: Episode VI Return of the Jedi. He explained that their inclusion was intended to enrich the depiction of the Sith, drawing inspiration from the style of an epic Greek poem.
In Star Wars Legends, the Dark Side user who instigated the movement against the Jedi, which eventually led to the Hundred Year Darkness, was known as Xendor. However, the first individual to hold the title of Dark Lord of the Sith was Ajunta Pall.