Sith Overlords were the traditional leaders of the Sith species. They battled against each other regularly to achieve the superior title of Sith'ari, although after the reign of Darth Bane and creation of the Rule of Two, that term came to mean god, perfect being, or prophesied one, and the "Sith Overlords," as such, died away.
Prominent early Sith Overlords included Adas and Dathka Graush. Holders of the title often included members of the Massassi caste. Some among the Sith priest class, the Kissai, who interpreted the death of their Sith'ari (King Adas) as a sign to reject the Sith point of view of the dark side of the Force, were banished as heretics from the Sith homeworld of Korriban—following their instincts to the Force-soaked world of Tund.
The Sith Overlords stayed in power over several planets from about 100,000 BBY to about 25,000 BBY, but were primarily sedentary and rarely strayed from their home planets of Korriban and Ziost.